Kenya's political rivals agreed Thursday to write a new constitution within a year as part of a deal to end post-election violence that already has killed more than 1,000 people, a government negotiator said.

In Washington, President Bush said he will dispatch Secretary of State Condoleezza Rice to Kenya to demand an immediate halt to violence that broke out after the disputed Dec. 27 presidential election.

Former U.N. chief Kofi Annan, who is mediating in the Kenya crisis, has hammered out a deal between the rival camps, a spokesman said earlier Thursday. But the full details have not yet been released.

"The two parties agreed to write a new constitution," government negotiator Mutula Kilonzo told The Associated Press after two days of secret talks were adjourned until Monday.

Kenya's current constitution was crafted in the lead-up to independence from Britain in 1963 and has been revised repeatedly, giving the president sweeping powers. Kenyans have repeatedly said they want a constitution that would reform how their country is run following decades of abuses by successive governments.

Kilonzo did not give details of any other aspects of the agreement, which is likely to be just a first step in negotiations. He spoke just hours after a spokesman for Annan announced the sides had signed a deal but gave no details.

Annan and the negotiators have been holed up in an undisclosed location for two days to try to hammer out agreements following a dispute over who won the election.

Opposition leader Raila Odinga accuses President Mwai Kibaki of stealing the vote, and domestic and international observers have said it was deeply flawed. The election unleashed weeks of violence, killing more than 1,000 people and forcing 600,000 to flee their homes.

The conflict has drawn international condemnation, with several countries threatening to cut aid, impose travel bans or freeze the assets of anyone suspected of inciting violence.

Rice and Assistant Secretary of State for African Affairs Jendayi Frazer plan to travel on Monday to Nairobi, where they will meet Kibaki, Odinga and civic leaders.

Bush said Rice will deliver a message directly to Kenya's leaders and people: "There must be an immediate halt to violence, there must be justice for the victims of abuse and there must be a full return to democracy."

He made the announcement during a speech previewing his six-day trip to Africa. Bush's schedule does not include a stop in Kenya.