UN pleads with Serbs to halt new assault: Bosnia's capital fears it now faces what may be the final, brutal battle as the fighting escalates and 4,000 shells hit the city

THE United Nations force commander in Bosnia has rushed to a small town south of Sarajevo to demand that the Bosnian Serb commander, Ratko Mladic, calls off what UN officials say is a decisive Serb push on the city.

General Francis Briquement of Belgium headed for Kalinovik, 40kms (25 miles) south of the Bosnian capital, after announcing he would demand that Gen Mladic stop a three- pronged offensive against Sarajevo, which is ruining the chances of Bosnian peace talks resuming in Geneva this weekend. The Security Council has denounced the Serb assault on the city on Thursday.

'We are seeing a concerted Serb attack on Sarajevo from the north, the north-west and west, with continuous fighting around Mount Igman,' said Barry Frewer, a UN spokesman.

Almost 4,000 shells landed on the city on Thursday in one of the worst bombardments for months. A Bosnian Serb commander said the attack on Mount Igman aimed to slice Bosnian Muslim supply lines of arms and food, which run from the city across the mountain to Croat-held regions in the south-west. He boasted that Serb forces would soon be parading down the main street.

The mainly Muslim Bosnian leadership said the fighting made it impossible to attend the Geneva talks - on the partition of the republic into three ethnic mini-states - with Bosnian Serbs and Croats and international mediators.

Bosnia's Muslim president, Alija Izetbegovic, has said he will attend talks only when Serbs halt offensives on Sarajevo, Brcko and Gorazde.

The Bosnian Serb leader, Radovan Karadzic, said the talks would be an 'inevitable failure'. He suggested they be delayed until autumn.

Mortar rounds and rocket explosions rocked Sarajevo yesterday as the intense fighting around Mount Igman engulfed the Rajlovac district, north of the city. A big infantry offensive by Serb forces appears directed at Zuc hill, which fell to Muslim-led Bosnian forces in January.

If the Serbs retake the hill, they will be in a position to resume random sniping and bombardment of crowded residential districts in New Sarajevo.

Mount Igman's fall to Serb forces threatens to spark an exodus of up to 32,000 Muslim refugees from the area into the city, where housing is already in short supply, utilities have broken down, and spare food supplies simply do not exist. 'If they flee into the city, it will pose a major challenge to us to find them shelter, with only four months before winter,' said Peter Kessler, a UN aid spokesman.

It is still far from clear whether the latest Serb assault, noisy as it is, presages the long-awaited final assault on Sarajevo, or whether the Serbs are simply battering away at the city in order to force Mr Izetbegovic to sign up to the partition plan.

In central Bosnia, 12 British doctors attached to British UN forces reached the small town of Fojnica, on a mission to save the lives of 230 mentally retarded children. The area has been ravaged by months of warfare between Muslims and Croats, with the more numerous Muslims gaining the upper hand. Four children have already died from malnutrition in the hospital in Fojnica, which fell to a Muslim offensive last week.

UN refugee officials fear more children will die in the next few days. Staff at the hospital fled, leaving children strapped to soiled cots, unattended for days. An unidentified virus threatens to kill more of the children, all severely weakened by malnutrition. The only good news was that a UN food and medical convoy crossed Serb lines into the Muslim enclave at Gorazde in eastern Bosnia, while Bosnian Croats lifted a ban on convoys entering central Bosnia.

Willy Claes, the Belgian Foreign Minister and European Community envoy, left Belgrade disappointed after the Serbian leader, Slobodan Milosevic, refused to see him. Mr Claes had hoped to persuade Mr Milosevic to help stop the warfare in Bosnia. He threatened further sanctions against Serbia and Montenegro if Serb attacks continued. Mr Claes said on his return to Brussels that he would discuss the crisis with other international leaders.

But with most of Serbia's war aims in Bosnia and Croatia achieved, Mr Milosevic appears to feel no need to play ball with Western diplomats.