Bosnia Leader Puts Brakes on Peace Talks : Balkans: He demands that Serbs withdraw from strategic peak close to Sarajevo. Serbs are said to pledge withdrawal.

ZAGREB, Croatia —  As the world waited to see if the United States could drum up support for a military strike in the Balkans, Bosnia’s leader slammed the brakes on peace talks Monday, demanding that the Serbs relinquish a strategic peak outside Sarajevo.

“If they don’t withdraw, we will postpone again the negotiations,” a resolute President Alija Izetbegovic told reporters at the meetings in Geneva.

The Bosnians say that Serb fighters stormed the summit of Mt. Bjelasnica on Sunday, in violation of a cease-fire declared two days earlier. The peak’s value lies in its proximity to another mountain, Igman, which dominates the city’s western approaches.

According to a spokesman for the Geneva negotiations, John Mills, Bosnian Serb leader Radovan Karadzic pledged that a withdrawal will take place. He said U.N. forces would assume control of the rugged heights near Sarajevo in the Serbs’ place.

But Izetbegovic, who boycotted the negotiations in the morning and then returned after lunch, was not ready to accept on sheer faith a promise from the politician whose armed allies have seized control of about 70% of Bosnia’s territory. He gave the Serbs until 10 a.m. Geneva time today to make good on Karadzic’s promise, reports said.

Izetbegovic, who presides over the Muslim-controlled Bosnian government and is the biggest loser in the three-sided civil war, went reluctantly to Geneva. He is worried that a partition of Bosnia will leave the Muslims crammed into a small landlocked enclave between bigger Serb and Croat territories that will ultimately be unified with Serbia and Croatia.

Peace talks and cease-fire notwithstanding, fighting continued in Bosnia on Monday, although Sarajevo itself was quiet.

Muslim-Serb fighting was reported in the northern city of Brcko, while Croats and Muslims were said by U.N. officials to be battling for the key central city of Gornji Vakuf. According to some reports, the Muslims successfully overran the city.

The fighting poses continuing danger to the success of the Geneva negotiations, warned Mills, the spokesman of the talks. All three parties lodged official complaints about cease-fire violations, he said.

“It would be a tragedy at this stage if the talks were to collapse, because we have the prospect of a settlement here,” Mills said.

The continuing warfare is also hampering international efforts to relieve suffering caused by the fighting and by “ethnic cleansing.” Thousands of people in Bosnia, many of them refugees fleeing the fighting, now lack food and water, aid officials say.

Peter Kessler, spokesman for the U.N. high commissioner for refugees, announced to reporters in Sarajevo that because of the fighting between Muslims and Croats, no aid trucks will leave the agency’s depot near the Croatian coast.

Elsewhere in the patchwork of ethnic and military tensions that once was the Communist dictatorship of Yugoslavia, rebel Serbs in Croatia scored a direct hit with artillery on a key pontoon bridge linking the Dalmatian shoreline with northern Croatia.

The Serbs, who shot at the bridge over the Maslenica inlet on Sunday, fired at least five more artillery shells at it Monday.