The Sudanese government and rebels accused each other today of violating a temporary cease-fire by launching attacks in southern Sudan.

The Sudanese Embassy in Nairobi said rebels led by Peter Gadet, a militia leader who is allied with the Sudanese People's Liberation Army, attacked two villages, Koch and Thorken, in oil-rich Upper Nile province on Thursday.

Koch, 50 miles south of Bentiu -- a government-held oil town -- and nearby Thorken are controlled by a government-backed militia, the embassy said in a statement.

But rebel spokesman Samson Kwaje denied the allegations and said government helicopter gunships attacked Rier and three nearby villages in the province on Thursday, killing as many as 20 people. He suggested that the government was "reacting to our complaint."

Neither side's claims could be independently verified.

The government and the rebels, who are holding talks in Kenya, signed the cease-fire agreement on Oct. 15. It took effect the following day and was to cover the entire country for as long as the negotiations aimed at ending the civil war continued.

Lt. Gen. Lazaro Sumbeiwo of Kenya -- an envoy with the regional Intergovernmental Authority on Development, which is mediating the talks -- said he was unaware of the latest claims. He said the talks were "going very well," but the Sudanese government warned that the fighting could threaten the cease-fire agreement.

"If the [government] troops are compelled to intervene or thus drawn into any new fighting over there, this could do away with the memorandum of understanding altogether," the embassy statement said.

Kwaje said the rebels would continue negotiating. "I do not think we are going to pull out of the talks," he said. "That is what the government wants, but we are serious about peace."

Civil war broke out in 1983, when rebels seeking greater autonomy in the south took up arms against the predominantly Arab Muslim government. An estimated 2 million people have died during the conflict, mainly through war-induced famine.

The United States has stepped up pressure on the Sudanese government, with President Bush signing a resolution Monday threatening sanctions if the government does not negotiate in good faith with the rebels.

In Geneva today, the president of Sudan, Lt. Gen. Omar Hassan Bashir, said the resolution, called the Sudan Peace Act, could undermine the cease-fire deal.

"The Sudan Peace Act is in fact a Sudan War Act," Bashir said. "It puts the government and the [rebels] on an equal footing, and it's giving [the rebels] an incentive whether there's peace or war," he said, because it would only punish the government.

U.S. officials in Geneva said that any penalties against the Sudanese government would be waived if the rebels were found to be at fault during negotiations.