Geneva ? His time at the helm of the world body nearing an end, U.N. Secretary-General Kofi Annan stepped up his efforts Tuesday to force a halt to atrocities in Darfur, demanding the U.N. Human Rights Council send an independent team of investigators to the volatile Sudanese region.

Annan, whose 10-year stewardship of the United Nations ends Dec. 31, was joined by top U.N. officials and agencies increasingly frustrated in their efforts to bring relief to people suffering from nearly four years of bloodshed.

“It is urgent that we take action to prevent further violations, including by bringing to account those responsible for the numerous crimes that have already been committed,” Annan told the 47-nation council’s emergency session on Darfur. The body is expected to decide today whether to pass a resolution, which would be nonbinding but increase political pressure.

Annan said militias were attacking defenseless civilians in Darfur and that “large numbers of women” were being raped.

“I urge you to lose no time in sending a team of independent and universally respected experts to investigate the latest escalation of abuses,” he said in a recorded video address opening the meeting.

Annan stopped short of singling out the Sudanese government, but said the council should send “a clear and united message to warn all concerned, on behalf of the whole world, that the current situation is simply unacceptable and will not be allowed to continue.”

But Louise Arbour, the U.N. high commissioner for human rights, cited “credible evidence” that the Sudanese military was responsible for ground attacks and aerial bombardments of civilians.

The Sudanese government also is accused of unleashing the janjaweed militia to help its forces counter ethnic African groups who rebelled in 2003. More than 200,000 people have been killed and some 2.5 million people have fled their homes, according to U.N. estimates.

Annan’s outspoken humanitarian chief, Jan Egeland, warned that “several hundred thousand lives will be at risk” unless they are protected from militia attacks.

This may be “the last opportunity for this council, the government of Sudan, the African Union and all of us to avert a humanitarian disaster of much larger proportions,” Egeland told the council Tuesday, his last day on the job.