You can smell death in Mostar. On the streets the stench of rotting corpses mingles with the odor of excrement and garbage. The public park has been converted into a cemetery, with some 75 fresh graves. A short sprint across one of the town’s many “sniper alleys” and you come to the chaotic Ratna Bolnica Hospital, where men, women and children writhe on soiled sheets, hideously wounded. A sister and brother, Selma Handzar, 9, and Mirzad, 8, lie next to each other. They were hit by Croatian mortars. “I no have -how do you say?-arm,” says Selma, trying her best in English. Mirzad is in danger of losing a leg. Next to them is a boy in a coma; his mother slumps on a corner of his bed, overcome by exhaustion. Nearby, Ramzi Salcin lies gasping for life through a plastic tube. Shrapnel from the Croats tore apart the head of the tall, muscular soldier. “His chances are poor,” says his surgeon. Sure enough, two minutes later, Ramzi dies.

Mostar, known for its graceful 16th-century Turkish bridge across the Neretva River, is a strategic prize in the brutal struggle between Muslims and Croats. The battle has been raging across central and southern Bosnia for the last four months. Before that, Muslims and Croats fought together to drive out the Serbs, whose shelling caused much of the vast destruction visible on both sides of the Neretva. But now that the Serbs have won control of more than 70 percent of the republic’s territory, the war in Bosnia has become a battle for second place between the Croats and the Muslims. The Croats want Mostar to serve as the capital of what they call “the Croatian community of Herceg-Bosna.” The Muslims are holding out for at least the eastern half of the city as part of a corridor to the Adriatic Sea, a lifeline for the proposed Muslim state being carved out in the peace talks in Geneva.

Last week U.N. forces stumbled into the middle of the struggle for Mostar. The United Nations dispatched a 27-truck convoy with more than 200 tons of food and medicine mainly to relieve the Muslims, who hadn’t received any aid for more than two months. But soon the 163 soldiers from Spain and Belgium, U.N. diplomats and sundry journalists became unwitting players in a dangerous partisan game.

First, Bosnian Croat forces refused to allow the convoy into eastern Mostar. They relented only after an agreement was made to exchange dead soldiers with the Muslims. But as the U.N. trucks rumbled toward the city on Wednesday, hundreds of Croatian women and children in the town of Citluk formed a roadblock, insisting that the vehicles be searched for weapons. Finally, in the predawn hours on Thursday, the convoy got through.

Then it was the Muslims’ turn to exploit the convoy for political and military advantage. After delivering aid and attempting to leave the eastern half of Mostar, the Spanish-led convoy found its way barricaded by Muslim demonstrators, who demanded permanent U.N. protection from the Croats. This was no spontaneous protest: reporters saw Bosnian soldiers dragging people out into the streets, where they carried posters written in official-style handwriting. Spanish officers said that Muslim soldiers threatened to shoot them if they tried to depart. Still, the fear of local residents was genuine. just days earlier, the Croats had shelled a Muslim enclave on the western side of the Neretva and appeared to be preparing a new offensive. “Desperate people do desperate things,” said a U.N. diplomat on the scene. “If I were in their shoes, I wouldn’t want us to leave, either.”

At the weekend, the blockade of the convoy had become eerily festive. Bosnian soldiers strutted about with their weapons, while residents took to the streets, cadging cigarettes and candy from the Spanish troops. Tired, dirty and ironically dependent for food and water on the very population they had come to rescue, U.N. troops also had to absorb flashes of anger from a Muslim population that feels abandoned by the world. “Now you see how we live,” one woman taunted a Spanish soldier. On Saturday, after intense negotiation, the Muslims allowed journalists and U.N. relief workers–but not military personnel–to leave.

The standoff was every Western leader’s nightmare. “It’s a hostage-taking,” said Cedric Thornberry, a top U.N. civilian official, who had been one of those trapped in Mostar, Beyond using U.N. forces as a shield to protect civilians against the Croats, the Muslims were buying time to repair downed bridges across the Neretva and to prepare for further fighting. Mindful of the risk that the heavily armed Croats, whose tanks killed two children last week, would intimidate the convoy, NATO dispatched U.S. A-10 tank-killing planes to buzz, but not attack, the city. The incident encapsulated the weakness of Western Bosnia policy. Refusing so far to intervene with firepower, the West has limited its involvement to humanitarian aid. But by relying on lightly armed, neutral troops, it has disappointed and antagonized the intended beneficiaries and turned peacekeepers into potential pawns in a deadly ethnic game. The showdown, says the U.N. diplomat in Mostar, “was completely foreseeable.”

So was the outbreak of fighting in Mostar. It coincided with the emergence of a plan to partition Bosnia into three ethnic ministates. Once the West began to endorse the idea, forces on the ground started grabbing as much disputed territory as they could. This week Muslim, Croatian and Serbian leaders come to Geneva again to negotiate an end to war and consider a proposal to turn Mostar into a European Community-administered district. “After all this, I don’t believe it’s possible for us to live together anymore,” says Ado, who administers one of the communal kitchens that feed Muslims in Mostar. The West may have to rethink the role of peacekeepers to ensure they can actually do what they’re supposed to. Since the arrival of U.N. forces in Mostar, 30 civilians and soldiers have died.