'Stop the bombing or we'll die'

Nato's confrontation with the Bosnian Serbs reached its most dangerous level of the three-year war last night, with the Western alliance threatening more air attacks despite the Serbs' seizure of United Nations observers as human shields.

Bosnian Serbs sent a stark message to the world: fight on, and risk the lives of UN soldiers, or back down. The latter course will leave the Serbs triumphant over Nato; the UN mission in tatters; and the Bosnian government to fight on alone, still handicapped by an arms embargo.

The risk that the war might destabilise the West's relationship with Russia increased as President Boris Yeltsin demanded an end to Nato strikes. He was "gravely dissatisfied" that the West had not consulted Moscow on the use of force.

Bosnian Serb television yesterday showed dramatic footage, likely to be remembered among the defining images of the war, of UN military observers chained to poles beside ammunition dumps and key bridges. One Canadian captive - later identified as Captain Patrick Rechner, 32 - was shown speaking to his HQ by mobile telephone. He said: "If the bombing stops, we will be set free, otherwise we will be killed ... If the bombing starts again, I have been instructed to tell you that we will die for the sake of Nato."

Altogether, eight of the unarmed military observers were detained in Serb-held territory, 29 more are confined to quarters, and about 150 peace- keepers are blockaded into weapons collection sites. Last night the Defence Ministry in Paris said 21 French peace-keepers guarding a heavy weapons collection point had been seized and were being held hostage at a Serb control point outside Sarajevo.

France, which has the largest UN troop contingent in Bosnia, last night threatened to withdraw its soldiers if the United Nations did not take measures to protect them. The UN Secretary-General, Boutros Boutros-Ghali, said President Jacques Chirac telephoned him to say that he wanted a "new mandate for Unprofor and a new policy for Unprofor which would take into consideration the blue helmets on the ground". The UN chief did not say what the new policy would be. "We will have to present a report to the Security Council in the next few days," he added.

Earlier yesterday UN officials in Sarajevo suggested that safety of hostages could not be the only consideration of the international community.

"The [potential] hostages were factored in ... We stand by our line that they must be released unharmed," one official said. "But if the international community is prepared to underwrite a continuance down this path [of escalation], we are prepared to do it."

Most of the 3,500 British troops in Bosnia are in the Muslim heartland and not at risk from any Bosnian Serb action. There are, however, more than 300 in the Gorazde enclave which is surrounded by Bosnian Serb forces and could come under attack. The most immediate threat is not to British army units, which can and will defend themselves if attacked, but to the individual UN military observers, some of whom are dispersed in Bosnian Serb-held territory.

The critical question now is whether the West has any real options for bringing more pressure on the Bosnian Serbs, other than those that would force the withdrawal of UN peacekeepers in Bosnia. One senior UN source said that if Nato attacked more important targets than ammunition dumps, it would - apart from risking the lives of the hostages - destroy the fragile consensus that allows the UN to operate in the 70 per cent of Bosnia in Serb hands.

It seems inconceivable that - if the captives are not harmed - Nato would consider a decisive strike against the Bosnian Serb command, since this would signal all-out war, render the UN's mission impossible and cause a potentially catastrophic rift with Russia. Equally, limited air strikes against targets such as ammunition dumps make no real impact on the Bosnian Serb war effort and provoke them into acts such as the hostage-taking and bombing of civilians that occurred on Thursday and yesterday.

Nato launched attacks for the second successive day yesterday after Bosnian Serb forces lashed out with their artillery at UN-protected Muslim "safe areas" on Thursday night. Captain Jim Mitchell, a Nato spokesman in Naples, said 12 aircraft dropped 500lb and 1,000lb bombs on the site during the 45-minute raid yesterday morning. "The idea is to stop the loading of guns by depriving them of ammunition," he said.

The Bosnian Serb forces ignored another deadline yesterday for the removal of heavy weapons from the exclusion zone around Sarajevo. Bosnian Serb soldiers seized three big guns from a UN site 20 minutes after the deadline expired. They also fired artillery at apartment blocks in the city, killing three civilians and wounding 29, and sent four more shells into Tuzla. They also appear to have cut all water and electricity supplies to Sarajevo.

France has suffered 37 fatalities among Unprofor troops and Britain 13 out of a total of 162.