Others say a major debt sell-off by Tokyo is unlikely, but noted that the mere fact that questions are being raised speaks volumes about the risks involved in relying so heavily on foreign investors to fund US debt.

"This natural disaster in Japan concerns me that it could speed up what's coming, because they are the second leading buyer of our debt," Senator Rand Paul, Kentucky Republican, told The Washington Times. "Small degrees of differences in how much they buy of our debt, I think, can make a big difference in interest rates that we have to pay people to buy our debt."

With the federal government having piled up $14.2 trillion in debt, budget experts are warning that the country is on an unsustainable fiscal path. Congress, they say, must find cuts in all areas of the budget, while reforming the entitlement programs - Social Security, Medicare and Medicaid - that are the biggest drivers of national spending. Concerns about the financial plight facing Japan, which trails only China among foreign holders of US Treasury debt, aren't helping the picture.

That may be hard to fathom for the millions of American business owners and households now preparing their own returns, but low taxes are nothing new for G.E. The company has been cutting the percentage of its American profits paid to the Internal Revenue Service for years, resulting in a far lower rate than at most multinational companies.

Its extraordinary success is based on an aggressive strategy that mixes fierce lobbying for tax breaks and innovative accounting that enables it to concentrate its profits offshore. G.E.'s giant tax department, led by a bow-tied former Treasury official named John Samuels, is often referred to as the world's best tax law firm. Indeed, the company's slogan "Imagination at Work" fits this department well. The team includes former officials not just from the Treasury, but also from the I.R.S. and virtually all the tax-writing committees in Congress.

While General Electric is one of the most skilled at reducing its tax burden, many other companies have become better at this as well. Although the top corporate tax rate in the United States is 35 percent, one of the highest in the world, companies have been increasingly using a maze of shelters, tax credits and subsidies to pay far less.

Some of them, he said, are "today are on the front lines in Adjabiya". Mr al-Hasidi insisted his fighters "are patriots and good Muslims, not terrorists," but added that the "members of al-Qaeda are also good Muslims and are fighting against the invader".

His revelations came even as Idriss Deby Itno, Chad's president, said al-Qaeda had managed to pillage military arsenals in the Libyan rebel zone and acquired arms, "including surface-to-air missiles, which were then smuggled into their sanctuaries". Mr al-Hasidi admitted he had earlier fought against "the foreign invasion" in Afghanistan, before being "captured in 2002 in Peshwar, in Pakistan". He was later handed over to the US, and then held in Libya before being released in 2008.

"The Islamists of al-Qaeda took advantage of the pillaging of arsenals in the rebel zone to acquire arms, including surface-to-air missiles, which were then smuggled into their sanctuaries in Tenere," a desert region of the Sahara that stretches from northeast Niger to western Chad, Deby said in the interview.

"This is very serious. AQIM is becoming a genuine army, the best equipped in the region," he said. His claim was echoed by officials in other countries in the region who said that they were worried that al-Qaeda in the Islamic Maghreb (AQIM) might have acquired "heavy weapons", thanks to the insurrection.

"We have sure information. We are very worried for the sub-region," a Malian security source who did not want to be named said. AQIM originated as an armed Islamist resistance movement to the secular Algerian government. It now operates mainly in Algeria, Mauritania, Mali and Niger, where it has attacked military targets and taken civilian hostages, particularly Europeans, some of whom it has killed. "We have the same information," about heavy weapons, including SAM 7 missiles, a military source from Niger said. "It is very worrying. This overarming is a real danger for the whole zone," he added

The UN's nuclear agency has warned the crisis could go on for months. It is believed the radiation at Fukushima is coming from one of the reactors, but a specific leak has not been identified. Leaking water at reactor 2 has been measured at 1,000 millisieverts/hour - 10 million times higher than when the plant is operating normally.

"We are examining the cause of this, but no work is being done there because of the high level of radiation," said a spokesman for the plant's operator Tokyo Electric Power Co (Tepco). "High levels of caesium and other substances are being detected, which usually should not be found in reactor water. There is a high possibility that fuel rods are being damaged," the spokesman added.

Meanwhile, the Japanese government said that airbone radiation around the plant was decreasing. Four of the reactors are still considered volatile.

The daily amount of caesium-137 released from Fukushima Daiichi is around 60 per cent of the amount released from Chernobyl. The difference between this accident and Chernobyl, they say, is that at Chernobyl a huge fire released large amounts of many radioactive materials, including fuel particles, in smoke. At Fukushima Daiichi, only the volatile elements, such as iodine and caesium, are bubbling off the damaged fuel. But these substances could nevertheless pose a significant health risk outside the plant.

"This is not surprising," says a researcher "When the fuel is damaged there is no reason for the volatile elements not to escape," and the measured caesium and iodine are in the right ratios for the fuel used by the Fukushima Daiichi reactors. Also, the Fukushima plant has around 1760 tonnes of fresh and used nuclear fuel on site, and an unknown amount has been damaged. The Chernobyl reactor had only 180 tonnes

The organisation set up to verify the Comprehensive Nuclear-Test-Ban Treaty (CTBT) has a global network of air samplers that monitor and trace the origin of around a dozen radionuclides, the radioactive elements released by atomic bomb blasts - and nuclear accidents. These measurements can be combined with wind observations to track where the radionuclides come from, and how much was released. The amounts being released are "entirely consistent" with the relatively low amounts of caesium and iodine being measured in soil, plants and water in Japan, because so much has blown out to sea. The amounts crossing the Pacific to places like Sacramento are vanishingly small - they were detected there because the CTBT network is designed to sniff out the tiniest traces.

Iodine is rapidly absorbed by the thyroid, and leaves only as it decays radioactively, with a half-life of eight days. Caesium is absorbed by muscles, where its half-life of 30 years means that it remains until it is excreted by the body. It takes between 10 and 100 days to excrete half of what has been consumed.

While in the body the isotopes' radioactive emissions can do significant damage, mainly to DNA. Children who ingest iodine-131 can develop thyroid cancer 10 or more years later; adults seem relatively resistant. A study published in the US last week found that iodine-131 from Chernobyl is still causing new cases of thyroid cancer to appear at an undiminished rate in the most heavily affected regions of Ukraine, Belarus and Russia.

Contaminated water likely seeped through the containment vessel protecting from the reactor's core, said Hidehiko Nishiyama of the Japan nuclear and industrial safety agency. Three men working inside the No. 3 reactor stepped into water this week that had 10,000 times the amount of radiation typical for that locale, Nishiyama said. That water likely indicates "some sort of leakage" from the reactor core, signaling a possible break of the containment vessel that houses the core.

The containment vessel is designed to prevent radioactive material from escaping into the atmosphere, even if other parts of the reactor are damaged. A rupture in the containment vessel could pose problems for workers who are trying to prevent that, depending on its severity. The three workers who were exposed to radiation by stepping in the contaminated water had the highest levels of radiation recorded so far, said Tokyo Electric Power Co, which owns the plant.

The incident raised questions about radiation control measures at the plant as 536 people - including government authorities and firefighters - continued working there Friday, according to an official with Tokyo Electric.

Soldiers fired in the air to hold back Saleh loyalists when they tried to march on the opposition rally. In his speech, the president - who has been in office for more than three decades - condemned bloodshed but also urged his supporters to "stand firm". He earlier denied that government forces had played any part in the shooting of demonstrators last week. Amnesty International has warned the government against any further use of "deadly force", saying: "The government cannot just shoot its way out of this crisis."

Both the government and opposition have set up checkpoints in Sanaa and the streets are full of armed men. There is real fear of a new confrontation, a BBC correspondent reports from the city. According to an AFP news agency report, Friday's crowds number in the hundreds of thousands.

President Saleh, dressed in a smart suit and sunglasses, took the microphone before a huge crowd. "We don't want power but we need to hand power over to safe hands, not to sick, resentful or corrupt hands," he said. "We are against firing a single bullet and when we give concessions, this is to ensure there is no bloodshed," he added. "We will remain steadfast and challenge them with all power we have."

Some Saleh loyalists were carrying guns and waving traditional Yemeni daggers at Friday's rally, Reuters news agency reports. Amnesty International responded on Friday by saying: "After the horrific killing of dozens of protesters last Friday, it is incredibly disturbing that Yemen's leaders have given the security forces more powers through a new emergency law instead of reining them in."

Yemen is one of a number of countries in the region that have seen unrest since the presidents of Egypt and Tunisia were ousted in popular revolts.

It was not immediately clear how Rabbi Shmuel Rabinovitz and Israeli lawmaker Danny Danon responded to Palin's puzzler. But the issue of public prayer is touchy at the Temple Mount because the site is holy to both Jews and Muslims. Palin, a failed GOP vice-presidential candidate, arrived in Israel on Sunday after a visit to India.

"Israel is absolutely beautiful and it is overwhelming to see and touch the cornerstone of our faith and I am so grateful to get to be here," said Palin, a Born Again Christian. "I'm very thankful to know that the Israeli and American link will grow in strength as we seek peace along with you."

Palin, who is due to meet later Monday with Prime Minister Benjamin Netanyahu, is the latest GOP possible presidential candidate to seek an audience with the Israeli leader. The former Alaska governor has been criticized for being a lightweight when it comes to foreign policy.

One of the effects of relatively high inflation is to ease the burden of debt by reducing its real value. For a highly indebted nation such as Britain, inflation therefore seems to make sense as an economic strategy. With no control over their own monetary policy, the Portuguese and other fiscally-challenged eurozone nations don't have that luxury. Without inflation to do the work for them, the austerity required to get public debt under control becomes that much greater, which is one of the reasons why Portugal will soon be following Greece and Ireland into seeking a bail-out. Britain, by contrast, gets a relatively pain-free way out of the mire.

One of the biggest shockers from the detail of Thursday's OBR (Office for Budget Responsibility) assessment is the escalating amount of money going straight down the drain of debt servicing costs. As public debt rises, these payments rise from 30.9 billion pounds last year to 66.8 billion pounds in 2015/16, or from 4.6 per cent to 8.8 per cent of all government spending.

Worse, these numbers are an understatement of the true position. According to data aired at a Taxpayers' Alliance seminar on Thursday, once private finance initiative payments, public sector pensions and other off-balance sheet liabilities are taken into account, the true size of the interest bill will be more like 200 billion pounds by the end of the Parliament. I won't trouble you with the projected costs of social security and tax credits, but they are little less alarming.

Still, Buffett said he believes there will be "huge efforts" put forth to preserve the euro. In the meantime, struggling peripheral countries like Portugal must find a way to resolve fiscal crises. "You can't have three or four or five countries that are in effect free-riding on the other countries. That won't work over time - they have to get their fiscal houses in reasonable harmony," he said.

The widely-watched investor spoke as yields on Portuguese bonds soared to new highs and markets remained alert for a potential European Union bailout of the troubled nation. Late Wednesday, Portugal's prime minister stepped down after the country's parliament rejected a fiscal austerity plan proposed by his government. "It isn't the end of the world, but alot of adjustment would be needed if the euro proved to be in real trouble," he said.

They were camped out next to the Interior Circle, or Gamal Abdel Nasser Square, in the capital. At nightfall, police attempted to disperse the youths and cut off electricity on the square around 11:00 pm (2100 GMT), an AFP journalist witnessed.

"A group of nearly 50 loyalists who were gathered not far from them (the students) took advantage of the power cut to throw rocks at the youths," one of the protesters, Moaz Kassrawi, told AFP. "Most of those injured suffered head wounds and had to be hospitalised," he said. According to another witness, police who had surrounded the sites did not intervene.

The White House signalled it was preparing for a change in power in Yemen, where it has been allied with the government of Ali Abdullah Saleh, president. Nato allies reached a deal in which the alliance will take over command of the Libyan no-fly zone, although responsibility for strikes on forces loyal to Colonel Muammer Gaddafi will not immediately come under the Nato umbrella.

Drawing a parallel between the unrest in Syria and the protests that unseated Hosni Mubarak, Egypt's former president, Mr Gates said: "I've just come from Egypt, where the Egyptian army stood on the sidelines and allowed people to demonstrate and in fact empowered a revolution. The Syrians might take a lesson from that."

His comments came as thousands of people marched on Thursday in Dara'a, southern Syria, where at least 44 people are now thought to have been killed in a week of protests, and as Mr Assad announced salary increases and promised greater freedom. "I would say that what the Syrian government is confronting is in fact the same challenge that faces so many governments across the region, and that is the unmet political and economic grievances of their people," Reuters quoted Mr Gates as saying during a trip to Israel.

Egypt is due to hold parliamentary elections in September, but the young political activists who launched the revolution have been pressing for a longer transition to allow them to organise. Politicians and analysts say only the Muslim Brotherhood opposition and remnants of Mr Mubarak's National Democratic Party are sufficiently prepared for elections.

Iron Dome is designed to defend against rockets at a range of 4-70 km and each battery consists of a multimission radar manufactured by Israel Aerospace Industries and three launchers, each equipped with 20 interceptors named Tamir. The main problem is that the Defense Ministry has so far only purchased and received two Iron Dome batteries, each of which can protect an urban area of approximately 100 square kilometers.

Since the escalation in hostilities in the South, Deputy Chief of General Staff Major-General Yair Naveh has held a number of discussions with IAF and Operations Directorate representatives in an effort to speed up the deployment and begin to use the system to protect Israeli civilians. On Thursday, the IDF decided to speed up the deployment of the system, possibly as early as next Sunday or Monday.

"Roads are also closed. According to the information that we have, more than 130 buildings collapsed because of the quake. There might be more casualties and damage." The BBC understands that the districts of Baan Thadeua and Baan Laen, within a 40km radius of Tachilek, have been worst hit. Cracks are visible in roads and rice fields have been wrecked by rising silt and water.

On the Thai side of the border, paddy fields and temples from Chaengsaen to Mae Sai have been damaged. A Burmese official told AFP news agency that 25 people had been killed in the town of Tarlay alone. The official said five monasteries and 35 buildings in the town had collapsed and that roads in the area had been damaged, making access for rescue parties difficult. The BBC's Rachel Harvey in Bangkok said it could be a while before the extent of the damage is known.