The United States has decided to throw its crucial support behind moves to establish a special United Nations commission to investigate alleged war crimes perpetrated by the military rulers of Myanmar.

Myanmar is the south-east Asian country formerly known as Burma.

In what represents a marked rollback of one of President Obama's most controversial foreign policy initiatives, US officials said Washington would now back the war crimes investigation, as urged earlier this year by the UN special rapporteur for human rights in Myanmar.

Washington is also said to be considering tightening sanctions against the junta.

The decision represents a reversal of an initiative announced last year to try to develop closer diplomatic ties with Myanmar by establishing regular meetings involving a senior US official.

There was talk that a closer relationship could possibly be rewarded with a dilution or dropping of some sanctions. But reports suggest Washington believes its overtures to the military have largely been rebuffed, even though several meetings have been held.

There is also likely concern over continued unconfirmed reports that Myanmar is interested in developing a nuclear weapon.

"There have been no positive results on democracy and human rights in our diplomatic engagement," one anonymous official told the Washington Post.

The decision by the US to back the tribunal, already supported by Britain and Australia, comes before elections in Myanmar on November 7.

While the junta, which changed the nation's name from Burma to Myanmar in 1989, claims they will be a stepping-stone towards full democracy, most observers in the West have dismissed them, saying they will do little more than cement the position of the military.

Campaigners have argued that the elections could not be considered fair while more than 2100 political prisoners - among them an opposition leader, Aung San Suu Kyi - were still detained.

Around 40 parties have registered to participate in November's elections, though many of them are groups led by former senior military officers who have taken off their uniforms for the process. The National League for Democracy, the party of Suu Kyi, a Nobel laureate, voted not to participate, though a breakaway group has registered.

Activists have welcomed the US decision. Aung Din, executive director of the Washington-based Campaign for Burma, said: "This is the right and timely action in response to the power-thirsty and brutal generals, who are expecting to delete their dirty crimes by putting a sham constitution into effect through a sham election.

"This is a clear message that the United States will not recognise their showcase election and will make them accountable for their horrible abuses against their own citizens."

Mark Farmaner, of the Burma Campaign UK, also supported the move but said it was essential that the European Union made a similar declaration. "The EU must end its silence on crimes against humanity in Burma, and publicly support a UN inquiry," he said.

Pro-democracy and human rights groups have urged the United Nations Security Council to impose an arms embargo on the regime and establish a commission of inquiry into crimes against humanity.

They fear a humanitarian crisis may develop along the border with Thailand, where Myanmar's military has been fighting ethnic Karens, pushing thousands of refugees across the border. Karen National Union fighters have been battling for half a century for greater autonomy from Myanmar's central Government.

The establishment of an independent tribunal to investigate war crimes is no small undertaking and has as much to do with geopolitics as with any offences that may have been committed.

Many activists opposed to the 2003 invasion of Iraq have campaigned for former British Prime Minister Tony Blair and former US President George W. Bush to be charged with war crimes.

In the case of Myanmar, five nations have so far supported an investigation. France is said to be one of several countries in the EU, with Germany, Austria and Italy, that support a softer stance.

In March, the UN special rapporteur for Myanmar, Toms Ojea Quintana, issued a report that was highly critical of the country's human rights situation. Urging an investigation, he said there was evidence of mass killing, torture, forced displacement and rape.

The decision by the Obama Administration also underscores concern that Asian giants such as India and China, which have warm relations with Myanmar, are securing valuable oil and gas deals.

Reports suggest there are various options for setting up a commission of inquiry. According to Foreign Policy magazine, the US could introduce a resolution establishing such a commission before the UN Human Rights Council, which will convene next month. Washington could also press the UN General Assembly to pass a resolution establishing it, or it could appeal to Ban Ki Moon, the UN Secretary-General, to do it under his own authority.

Such inquiries can often lead to war crimes prosecutions.

Myanmar's junta and its 77-year-old leader, General Than Shwe, could be investigated over a number of alleged crimes during its rule including:

* The crushing of the August 1988 democracy uprising that led to the deaths of 3000 to 6000 people.

* Widespread ethnic cleansing of groups such as the Karen, which have been fighting for greater autonomy for half a century.

* The alleged use of forced labour to build pipelines and other infrastructure, torture and beatings, and the use of rape by Myanmar's armed forces. Human Rights Watch says that such violations are widespread in Myanmar.

* The violent crackdown on the September 2007 "Saffron Uprising", headed by Buddhist monks, which left scores of people dead.

- Independent