The Bush administration declared for the first time yesterday that genocide was being committed in Darfur, blaming Arab militias and the Islamist government of Sudan for the atrocities. "Genocide may still be occurring," Colin Powell, the US Secretary of State, said.

The Bush administration declared for the first time yesterday that genocide was being committed in Darfur, blaming Arab militias and the Islamist government of Sudan for the atrocities. "Genocide may still be occurring," Colin Powell, the US Secretary of State, said.

"The situation on the ground must change and change quickly," he said. "There are too many tens of thousands of human beings who are at risk."

America's failure to halt the genocide in Rwanda in 1994 has haunted successive US administrations. Yesterday's declaration was not a commitment to intervene militarily to save lives in Sudan, leaving open the possibility that it was motivated as much by US presidential politics as humanitarian concerns.

Branding the atrocities genocide is important, however, as it carries legal and moral obligations under the Geneva Conventions. The genocide convention orders signatory states ­ including the US and Britain ­ to "prevent and punish" acts of genocide.

Questioned about the change in the American position last night on Channel 4 News, the Foreign Office minister, Chris Mullin, said: "It may well be genocide, and that is why we are supporting Colin Powell's call for the United Nations to investigate urgently. Whatever you call it, there is no doubt that grave crimes against humanity have been committed in Darfur."

Pressed on the genocide label, Mr Mullin said: "We ought not to get too bogged down in words. We shall be supporting Mr Powell's call for an urgent UN investigation. We want to see the toughest resolution possible. We have got to take the other members of the Security Council with us, please bear that in mind, but we will be in the forefront of the debate."

The Janjaweed militia, controlled by the Sudanese government, has been accused of killing 50,000 people in the 18 months that followed a rebellion by black African farmers in Darfur. More than one million people have been forced from their homes.

General Powell told the Senate Foreign Relations Committee: "We concluded that genocide has been committed in Darfur and the government of Sudan and the Janjaweed bear responsibility ­ and genocide may still be occurring."

He acknowledged the responsibilities under the Geneva Conventions on the prevention of genocide, which "to us, at this time, it appears that Sudan has failed to do". Consequently, he said, the UN should fully investigate the killings in Darfur with a view to establishing accountability.

General Powell based his statement on a State Department report by officials who interviewed 1,136 Darfur refugees over a five-week period in Chad. The report revealed a "consistent and widespread pattern of atrocities committed against non-Arab villagers" from the western region of Sudan.

Mr Mullin was asked whether British troops could be deployed to the region. He said: "It is too early to say that yet. We have some British advisers there but it is too early to go down that road. I shall be in Sudan for most of next week, and obviously I shall have a clearer picture then."

Britain and the US hope that the UN Security Council, which is considering a US draft resolution threatening oil sanctions against the Sudanese government, will agree to proposals in the draft for such an international inquiry. Similar commissions were set up after the 1994 Rwanda genocide and the Yugoslav conflict and eventually led to war crimes tribunals.

The European Union has refrained from declaring genocide in Sudan, maintaining that it is for the UN to decide. Kofi Annan, the UN secretary general, has described the Sudanese government's "scorched earth policy" as the world's greatest humanitarian disaster, but has not used the word genocide.

Aid agencies and rights groups expressed concern that the talks at the UN could stall at a time when there is a need for urgent action to resolve the humanitarian crisis. "It's good to see the US recognising the scale of the crisis but words are not enough," said an aid agency with humanitarian workers on the ground in Darfur.

The Sudanese deputy foreign minister, Najeib El-Kheir Abdel Wahab, said: "We don't think this kind of attitude can help the situation. We expect the international community to assist the [African Union peace] process that is taking place in Abuja and not put oil on the fire."