The U.S. Congress late Thursday night passed resolutions declaring that atrocities that have been unfolding in western Sudan (search) are genocide (search) and urged the Bush administration to do the same.

The resolutions came as U.S. Secretary of State Colin Powell met with U.N. Secretary-General Kofi Annan Thursday, for the second time in three weeks, to discuss what he called a "humanitarian catastrophe" in Darfur (search).

An estimated 30,000 civilians have been killed — most of them black Africans — and up to 1 million displaced since two groups from the Darfur region's African tribes took up arms over what they regard as unjust treatment by the government in their struggle with Arab countrymen over land and resources.

The Arab militia, called Janjaweed, began attacking black villages, and some human rights groups have accused the militias of ethnic cleansing and genocide.

But until the congressional resolutions late Thursday, U.S. officials had declined to label the killings a genocide. Passed unanimously in the House and Senate, the measures urge President Bush to call the situation in Sudan "by its rightful name" and urge his administration work with the international community to stop it.

A 1948 UN convention obligates the international community to prevent and punish acts it has declared as genocide.

U.S. officials and humanitarian groups accuse the Sudanese government of backing the militias — a claim Khartoum denies.