George Clooney has embarked on his latest role, as The Star who Went to Darfur, by modestly saying he felt uncomfortable about giving speeches on the political stage - or telling "people what they should or should not do".

The Oscar winner then proceeded to outshine the two leading senators flanking him at a packed Washington press conference yesterday as he told the US Government, the American people and the United Nations exactly what they should do about the genocide in Sudan.

Speaking on his return from making a short documentary film in Sudan and Chad with his father, Nick, a former TV news reporter, Clooney warned that time was running out to help some of the two million refugees displaced in the world’s biggest humanitarian crisis.

"Everyone has a good reason not to act," he said, "but we cannot turn away and look away and hope this will disappear, because if we do these people will do just that - disappear - and only history will be left to judge us."

He said the film was intended to keep the issue on the "front-burner" as long as possible. "It’s not easy to do...but that all I can do. I’m not a legislator or a politician, I just try to use the credit card you get from being famous in the right way."

Senator Barack Obama, seen as a future Democratic presidential candidate, and Senator Sam Brownback, a right-wing Republican who could run in 2008, both urged Congress and President Bush to do more about Darfur - where militias backed by Sudan’s Islamic fundamentalist government have killed tens of thousands of civilians since 2003.

Ahead of a mass rally in Washington and other cities this weekend, an unusually broad coalition of 164 groups, including Evangelical Christians such as Senator Brownback, are pressing for a multi-lateral peace-keeping force to end the violence.

Mr Clooney said that if Nato or the United Nations did not act then "I’m not quite sure what they are there for."

He suggested that America was "dancing around the issue" because it did not want to commit American troops on the ground. "So we’re going to have to build our alliances and find someone who is willing to do it."

Although he has been a vocal Hollywood critic of the Bush Administration in recent years, Mr Clooney cited the support of the two senators from opposite ends of the spectrum, as he said: "It’s not a political issue, it’s not left about left and right, conservative or liberal points of view. It’s only about right or wrong."

He described how tenuous the hold on life was for some of the refugees he had just met. "If you are lucky enough - and I mean lucky enough - to survive the Janjaweed militia and the killings and walk 50 miles to a refugee camp...then circling the camps are Janjaweed.

"Women go out to get wood for cooking that night get raped. Men don’t go because they would be killed. Older women are sent because they have less chance of being raped. It’s really that crass, you don’t understand - until you are standing there - that they have nothing."

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