U.N. Secretary-General Kofi Annan warned that Sudan's Darfur region was descending into complete lawlessness and called on the government and rebels to conclude peace talks by the end of the year.

In his monthly report to the Security Council on Monday, Annan said violence, killing and rape had increased in Darfur in September and October. Civilians have been forced out of villages, in some cases for the second or third time.

"The looming threat of complete lawlessness and anarchy draws nearer, particularly in western Darfur, as warlords, bandits and militia groups grow more aggressive," Annan wrote.

The only solution was to conclude by the end of the year a "framework peace agreement" in the forthcoming seventh round of African Union-led peace talks in Abuja, Nigeria, Annan said.

"It should be made clear to all parties that the AU-facilitated peace talks in Abuja are the only vehicle for achieving a viable solution," he said. "Talks outside of this framework, where some of the parties are excluded, will never lead to any sustainable agreements."

A new round of talks in Abuja was to begin on Monday, but Africa Union sources in Khartoum said negotiations were delayed for logistical reasons. Annan's report was written before that development.

Tens of thousands of Sudanese have been killed since a revolt in Darfur began in early 2003 by non-Arab villagers who accused the government of neglect and repression.

The government is accused of arming Arab militias, known as Janjaweed, who killed, raped, burned down villages and forced more than 2 million people out of their homes. Khartoum has denied supporting the militia.

The African Union has a monitoring force in Darfur, the only bulwark against violence. Five of its peacekeepers were killed in October by armed groups, presumably rebels.

In June, Annan reported that civilian deaths had dropped since early in 2005, but his new survey said this was no longer the case and the United Nations would give details next month.

But the report said it was clear violence had increased, including the killing of children, recruited as soldiers by all factions.

Assault and rape against women and girls is also on the rise, particularly in western Darfur.

In one case, two women told U.N. monitors of gang rapes outside of a refugee camps on October 2 by 10 armed men wearing khaki uniforms and riding horses and camels, a description that fits the Janjaweed.