NAIROBI, Kenya — The U.N. Security Council should impose sanctions on Sudan's government and enforce an arms embargo on pro-government Arab militias accused of ethnic cleansing in the country's Darfur region, a human rights group and aid agencies said Monday.

Sudan has failed to disarm and disband the Arab militias responsible for atrocities, instead absorbing some into its security forces "to 'guard' the camps of the very same displaced civilians whom they had originally burned out of their villages," Human Rights Watch said in its report.

Last week, one of those camps was forcibly dismantled by Sudanese forces, driving the people who sought refuge there back into Darfur's arid countryside, the group said.

The report, "If We Return We Will Be Killed," was released ahead of the Security Council's special session on Sudan opening in Nairobi, Kenya, on Thursday.

The United Nations says the Darfur conflict has created the world's worst humanitarian crisis, claiming at least 70,000 lives since March — mostly from disease, hunger and hardships from being uprooted. Many more have been killed in fighting since the conflict started in February 2003, but no firm estimate exists.

The conflict has driven 1.8 million people from their homes.

U.N. Secretary-General Kofi Annan told the Security Council on Nov. 3 there were strong indications that war crimes and crimes against humanity were committed "on a large and systematic scale" in Darfur.

But a Security Council draft resolution circulated at that time does not impose sanctions on Sudan "for its direct participation in the brutal ethnic cleansing of Darfur's civilians," Human Rights Watch said.

On July 30, the Security Council imposed an arms embargo on rebels and the pro-government Arab militia, known as the Janjaweed. The U.N. also ordered a freeze of assets held by the Arab militia and imposed a travel ban on their leaders.

"But the Janjaweed don't travel and they don't have assets abroad," and no sanction committee has been set up by the United Nations, Human Rights Watch's Jemera Rone said.

"The Sudanese government continue to supply them with weapons and back their attacks with helicopter gunships."

The Security Council should extend that arms embargo to the Sudanese government and impose travel sanctions and asset freezes on key government and military officials, the group said.

It also should ensure that displaced people can return home safely and that the government provide reparations — possibly from oil revenues — to victims, the organization said.

Meanwhile, six international aid agencies working in Sudan said Monday the humanitarian situation in Darfur is deteriorating. The groups also called for the Security Council to take stronger action.

"Previous U.N. resolutions on Darfur have amounted to little more than empty threats, with minimal impact on the levels of violence," said Cynthia Gaigals, speaking for a group of organizations including CARE International and Oxfam International.

"The Security Council must now outline specific and time-bound compliance measures and agree to implement them if there is no clear and sustained progress."

The violence in Darfur began when Sudan's Arab-dominated government was accused of unleashing Arab tribal militias against non-Arab African farmers after attacks by two rebel groups.