The top U.S. aid official has briefed the U.N. Security Council on Secretary of State Colin Powell's just-completed visit to the Darfur region of Sudan. The council is being asked to impose sanctions against Sudanese Arab militias blamed for widespread atrocities in Darfur.

U.S. Agency for International Development (USAID) Administrator Andrew Natsios came directly to the United Nations after accompanying Secretary of State Powell on his visit to Darfur.

Speaking to a closed-door Security Council meeting, Mr. Natsios called for sanctions against government-backed Arab militias known as Janjaweed. These militias are terrorizing black African villagers in Darfur.

Sudan, backed by African and Arab council members and Russia, has lobbied to keep the Darfur issue off the council agenda. Faced with mounting evidence of atrocities, several council members have urged a "go-slow" approach to sanctions.

But Mr. Natsios said that Washington wants immediate action unless the Sudanese government fulfills promises made to Secretary Powell that the Janjaweed would be curbed.

"We will not be waiting for [a] long time, because Secretary Powell made clear in his comments, in a press statement and to Sudanese leaders privately, and I was in on the discussions, that we're not talking about months, we're talking about days or weeks, a short period of time," he said.

Mr. Natsios said he had come directly to the Security Council because of the urgency of the potential catastrophe facing the more than one million displaced Darfurian villagers.

"Displaced people in Darfur told us repeatedly and told the staffs of all our organizations that the cities and the displaced camps have become prisons, they're concentration camps, where if we [AID officials] leave [they're] either raped or murdered," he added. "So we can't leave. The thing that makes this very different from all recent emergencies is that these populations cannot rely on traditional coping mechanisms for survival."

Mr. Natsios said the United States has spent $117 million on aid to Darfur in the past nine months and will spend another $150 million this year.

Secretary Powell's visit to Sudan coincided with one by U.N. Secretary General Kofi Annan. The combined visits were intended to draw world attention to the Darfur crisis, where aid officials say two million people are in desperate need of humanitarian assistance.

USAID Administrator Natsios said the daily death rate in some of the Darfur camps is six times higher than the international standard for declaring an emergency. Those figures, he said, already qualify western Sudan as a catastrophe.

And with the rainy season coming, Mr. Natsios says, there are likely to be outbreaks of meningitis and with water and sanitation systems in a state of collapse, he says death rates could get much worse in the weeks and months to come.