The United Nations should immediately deploy troops not only in Sudan's Darfur region but also in eastern Chad to stop ethnic conflict from spilling across the border, Amnesty International said on Thursday.

Tens of thousands of civilians in lawless eastern Chad have already fled increasingly brutal cross-border raids by Darfur's Janjaweed Arab militia, but the problem will only worsen if U.N. troops are sent just to Darfur, Amnesty's head Irene Khan said.

U.N. Secretary-General Kofi Annan travels to an African Union summit in Gambia this weekend to lobby Sudan's President Omar Hassan al-Bashir to relax his opposition to U.N. troops in Darfur. But Khan urged the United Nations not to forget Chad.

"They can't ignore eastern Chad: it is part of the same problem," Khan told Reuters in an interview, coinciding with the launch on Thursday of an Amnesty report on the region.

"If they sent peacekeepers just to Darfur, that would just push the militia across the border into Chad ... We have seen it in many other situations in Africa."

With talk of the United Nations taking over from an ineffective African Union force in Darfur, the Janjaweed have already begun to clear themselves a living space in eastern Chad by permanently seizing land there, Khan said.

"Things are getting worse. The situation in eastern chad is deteriorating rapidly," she said, citing testimony from Chadian refugees who fled Janjaweed raids and returned to find the militia had occupied their territory.

"They are saying the same things we heard in Darfur: 'You are slaves, this is our land'."

The Darfur conflict erupted in 2003 when non-Arab tribes took up arms against Khartoum, accusing the Arab-dominated government of neglect. Al-Bashir retaliated by arming the Janjaweed, who began a campaign of murder, rape and plunder.

Tens of thousands have been killed and 2.3 million people driven into squalid camps in Darfur and Chad. With Janjaweed raids stretching ever-deeper into arid Chad in recent months, Amnesty estimates some 10,000 Chadian refugees have fled into war-torn Darfur -- worsening the humanitarian disaster there.

"The people in Chad need protection right now. They should not be held hostage to the way Sudan is dragging its feet on negotiations for U.N. peacekeeping operations," Khan said, urging U.N. protection on the Chad border and in refugee camps.

African leaders should seize the opportunity of this weekend's summit in the Gambian capital Banjul to pile pressure on Sudan to accept a U.N. force for Darfur, using the threat of sanctions if necessary, Khan said.

"They need to be tough or they will have no credibility left as an effective instrument for promoting peace and security in Africa," she said.

The chairwoman of the AU's Peace and Security Council Nkosazana Dlamini-Zuma said on Wednesday the 53-nation body was ready to impose sanctions on any group undermining the peace process in western Sudan. One of three Darfur rebel groups and the Sudanese government signed a peace deal in the Nigerian capital Abuja on May 5.

The African Union has around 7,000 peacekeepers in Darfur to help promote peace, but its mandate prevents its from protecting civilians. A strengthened AU force with a tougher mandate could act as a bulwark against attacks until UN peacekeepers arrived in Darfur, Khan said.

A worrying development in eastern Chad was attempts by some villagers to acquire weapons to fight the Janjaweed, who forged alliances with some Chadian tribes. It is a situation bearing all the hallmarks of Darfur in 2003, Khan said.

"If those who are being attacked get hold of arms, then they are very likely going to resist other tribes in Chad, not just the Janjaweed, and it could actually lead to more bloodshed as one community turns against the other."