Serb Commander Claims Stranglehold on Sarajevo : Bosnia: Gen. Mladic says his forces have seized Igman Mountain, the missing link in his siege of the capital.

ZAGREB, Croatia — The commander of Bosnia’s Serbs announced Wednesday that Igman Mountain, the missing link in his 16-month attempt to strangle the city of Sarajevo, has been stormed and taken by his fighters.

U.N. officials said they could not confirm the boast by Gen. Ratko Mladic. Officials in Bosnia’s Muslim-controlled government said their forces were beaten back by the Serbs from two key positions on the peak southwest of Sarajevo and were in “critical shape” but holding fast.

Whatever the case, the battles on and around the mountain overlooking Bosnia’s capital made a mockery of a pledge by the Bosnian Serb political leader, Radovan Karadzic, that his forces would withdraw and put the high ground in the hands of U.N. peacekeepers.

Earlier this week, Mladic’s army overran neighboring Bjelasnica Mountain, chasing back Muslim fighters. U.N. officials fear a mass exodus as thousands try to flee the Serbian onslaught.

Asked if he was now in control of Igman, Mladic told Reuters Television: “Yes, sir. Both Bjelasnica and Igman. You should go to Igman and see for yourself.”

Mladic has refused to withdraw his troops from the mountains even after the order from Karadzic, saying that Serbs have never before surrendered territory they conquered.

The Geneva peace talks on Bosnia hung in the balance Wednesday as President Alija Izetbegovic announced that he would end his boycott protesting the Serbs’ sustained offensive. His absence has paralyzed negotiations on partitioning the republic into three zones--Serbian, Croatian and Muslim.

Karadzic and his Croatian counterpart, Mate Boban, announced that they were leaving Geneva on Wednesday night but may return Friday if there is some certainty of negotiations, Geneva conference spokesman John Mills said.

Izetbegovic’s return to the negotiating table hinges on Serbian compliance with a 24-hour deadline for their withdrawal from the key mountains. Diplomats said they believe Izetbegovic is delaying in the hopes of intervention by the North Atlantic Treaty Organization.

By pressing their offensive, the Serbs appear to be bent on seizing as much territory as they can, both to force Izetbegovic to resume talks and to be in the best possible strategic position if NATO does order air strikes to break the siege of Sarajevo.

At U.S. urging, the Western military alliance voted earlier this week to allow that step. And Wednesday, NATO’s commander in southern Europe, Adm. Jeremy Boorda, met in Zagreb for three hours with U.N. Gen. Jean Cot to discuss possible coordination of air strikes between NATO planes and peacekeeping forces on the ground.

NATO officials are supposed to meet again next Monday to consider military planners’ suggestions about where and when to strike. The warplanes, mostly American, are on standby in Italy.

Igman’s possession by the Serbs would deal a body blow to Sarajevo’s defenders, because it overlooks the city and dominates the last remaining supply route linking Bosnia’s capital with the outside world.

Far from acting like a soldier worried about NATO intervention, Mladic on Wednesday appeared to taunt the West, which many Serbs believe is bluffing when it threatens military action. The Serbian general had a Gazelle helicopter on Bjelasnica Mountain in violation of the U.N.-enforced flight ban over Bosnia, U.N. spokesman Cmdr. Barry Frewer told reporters in Sarajevo.

Mladic “is acting like a man who is questioning the extent that we will challenge him, or that the West will challenge him,” Frewer said.

Laura Silber in Geneva contributed to this story.