Sudan has not reined in Arab militias responsible for killing tens of thousands of black African civilians and displacing more than a million others in Darfur, casting doubts on its ability to meet a U.N. Security Council demand that it do so by Tuesday, according to senior U.N. diplomats and Human Rights Watch.

But the 15-nation council appears unlikely to impose threatened sanctions on Sudan, according to council diplomats who cited U.N. claims that Khartoum has cooperated with its efforts to address the humanitarian crisis. "I think there is a growing recognition that sanctions are not likely to be a productive approach," said Pakistan's U.N. ambassador, Munir Akram.

The Bush administration insists that sanctions remain an option but acknowledged that its immediate priority is to rally council support for an African Union proposal to bolster a small observer mission with thousands of additional African peacekeepers. The Nigerian-sponsored initiative is the subject of peace talks between Sudan and Darfurian rebels in Abuja, Nigeria. "If the government resists that, then, in my view, the United States will have no choice but to support sanctions," U.S. Ambassador John C. Danforth told the Associated Press this week.

The top U.N. envoy in Sudan, Jan Pronk of the Netherlands, said he would withhold judgment on Sudan's compliance with the resolution until he concludes a three-day tour of Darfur on Saturday and reports to the council next week.

Pronk attended a ceremony where hundreds of members of a uniformed, government-backed paramilitary group, known as the Popular Defense Forces, handed over their weapons.

The gesture comes after Tuliameni Kalomah, the United Nations' assistant secretary general for political affairs, told the council Tuesday that while Sudan had improved access for humanitarian aid workers, it had done "practically nothing" to stop the militias, according to a council ambassador who attended the closed-door briefing. The ambassador declined to speak publicly, citing the confidential nature of the discussions.

Kalomah credited Sudan with pledging to deploy thousands of additional police in Darfur and to begin establishing safe areas there by the end of the month, according to another diplomat who also attended the meeting. But Kalomah said the United Nations continues to receive reports that the militias are active in West and North Darfur, citing complaints by displaced civilians that they are attacked when they venture outside their camps, according to another diplomat. Kalomah said, according to the diplomat, that the Sudanese government has not provided the United Nations with a list of names and the size of militias, as it had promised.

"It's not a clear-cut picture," said another senior U.N. official, who said Sudan had probably done just enough to undercut the case for sanctions. "Are they cooperating? Yes, some ministers are really cooperating. Are they sabotaging us? Yes, others are really sabotaging us."

The latest crisis in Darfur began in February 2003, when two Darfurian rebel groups, the Sudanese Liberation Army and the Justice and Equality Movement, took up arms against the government, citing discrimination against the region's black African tribes. U.S. officials maintain that Sudan organized local Arab militias, known as Janjaweed, and supported them as they attacked hundred of villages, killing thousands and forcing more than a million from their homes.

Last month, the Security Council adopted a resolution demanding that Sudan "disarm the Janjaweed and apprehend and bring to justice Janjaweed leaders" responsible for atrocities. It called on U.N. Secretary General Kofi Annan to brief the council in 30 days and warned that it would consider "further action," including economic and diplomatic sanctions, if Sudan failed to comply.

Human Rights Watch asserted Friday that Sudan is permitting the militia to operate at least 16 military camps with "total impunity." "These militia continue to operate; they continue to base themselves out of camps in government-controlled territory; they continue to operate with government troops in attacks on civilians," said Leslie Lefko, a researcher at Human Rights Watch.

The international relief community -- which has seen the number of its workers in Sudan increase from 170 to more than 500 in recent months -- has stepped up its efforts to tackle the unfolding humanitarian crisis.