NAIROBI, Kenya - The largest United Nations peacekeeping force in the world is stretched to the limit as fighting in eastern Congo threatens to engulf the region, UN Secretary-General Ban Ki-moon said Friday.

"We must put the cycle of violence behind us," Ban said at a summit of seven African leaders, including Congolese President Joseph Kabila and Rwandan President Paul Kagame, who wields strong influence over Congolese rebel leader Laurent Nkunda.

The conflict between the government of Congo and Tutsi-led rebels, which has forced tens of thousands to flee their homes, is fueled by ethnic hatred left over from the 1994 slaughter of a half-million Tutsis in Rwanda and from Congo's civil wars.

Nkunda called a cease-fire last week but it appeared to be unraveling.

"This crisis could engulf the broader sub-region," Ban said.

European Union Development Commissioner Louis Michel, who has held separate talks with Kabila and Kagame in recent weeks, urged both sides to respect the cease-fire. But he said direct talks between Kabila and Kagame were not on the agenda Friday. Ban also has urged the two men to talk.

A top Africa official at the summit criticized the UN peacekeeping force -- known by its French acronym MONUC.

"MONUC has failed," said Eddie Kwizera, Ugandan President Yoweri Museveni's top aide on relations with Congo and other Great Lakes countries, referring to the peacekeeping mission of 17,000 troops.

The foreign minister of Tanzania, which chairs the African Union, said the leaders meeting in Kenya are considering whether to appoint an envoy to handle the crisis in Congo or start a process of mediation.

A spokesman for the UN mission, Madnodje Mounoubai, was quoted by UN Radio Okapi as saying peacekeepers were doing what they could to protect civilians.

"When the fighting started, the civilian population, en masse, came to find refuge around the (peacekeepers') MONUC base. So, the first thing that MONUC did was to assure these people who arrived around its base their protection and security," Mounoubai said.

Nkunda went on the offensive Aug. 28 in the eastern Congo province of North Kivu and brought his fighters to the edge of its largest city, Goma, last week before declaring a unilateral cease-fire. Tens of thousands of civilians fled the fighting and an unknown number were killed or injured.

Nkunda claims the Congolese government has not protected ethnic Tutsis from the Rwandan Hutu militia members who escaped to Congo after taking part in the 1994 Rwandan genocide.

All sides are also believed to fund fighters by illegally mining Congo's vast mineral riches, giving them no financial interest in stopping the fighting.