Rebels in the Darfur region of Sudan said Saturday that government forces and Arab militiamen have continued to bomb and torch villages and kill civilians -- with attacks on six villages in the past three days, including one that killed 64 people.

To protest the continuing violence, the rebels said that for 24 hours they would boycott the peace talks with the Sudanese government underway in Abuja, Nigeria.

Meanwhile, a U.N. team completed a mission that could determine whether Sudan will face international sanctions.

Security has improved in camps in the violence-torn Darfur region, but displaced villagers still face attacks and abuse when they leave their camps, a U.N. team said Saturday.

More than 1.5 million black African villagers have been driven from their homes by the militiamen known as the Janjaweed, who are allegedly backed by the government. Many of those people are now living in 147 camps scattered across Darfur, a region the size of France.

An estimated 50,000 people have been killed in the violence, which began in February 2003, when African rebel groups began an anti-government campaign. The latest attacks reported by the rebel negotiators could not be independently confirmed.

The United Nations has given Sudan until Monday to take actions to stop the militiamen or face possible sanctions. The government has said it is trying to restore security and denies any links to the Janjaweed.

Erick De Mul, who headed one of three U.N. fact-finding teams that have spent three days in the Darfur region, refused to say whether he expected U.N.-imposed sanctions.

De Mul, the U.N. deputy humanitarian coordinator, said he saw improvements in the camps.

Sudanese government negotiators said they couldn't confirm or deny the attacks and decried the rebel walkout. "It's very sorrowful," a delegation spokesman, Ibrahim Mohamed, said of the boycott. "We are here to negotiate and stop such painfulness."

The government says it has arrested an unspecified number of militiamen and sentenced some to death.

But Human Rights Watch, a U.S.-based advocacy group, accused the government of letting the militias maintain at least 16 bases in the region -- including five apparently shared with the military.

Earlier in the day, Sudan's government ruled out any discussion at the Abuja talks of an African Union proposal to send up to 2,000 peacekeepers into Darfur.