Firm message to Serbs from united West

NATO yesterday carried out its six-month-old threat to punish any attempts to remove impounded weapons around Sarajevo.

The launching of air strikes shows that some of the political problems that surrounded the use of force have been removed, and underlines Western determination to back UN forces in Bosnia. But it leaves open the question of how deeply the alliance will, or can, become involved in the conflict.

After the latest infringement of a UN Security Council resolution, the West clearly decided that the balance of possibilities favoured action rather than hesitation, which has frequently characterised its response before. The Bosnian Serbs had removed a tank, two armoured personnel-carriers and an anti-aircraft gun from a depot, near Sarajevo, where they had been placed during the demilitarisation of the city in February. Bosnian Serb forces were reported to have subsequently fired upon a pursuing UN helicopter.

The alliance first threatened the use of force almost exactly a year ago, to prevent the 'strangulation of Sarajevo'. This became a reality only in February, when a detailed plan for demilitarising the area was drawn up, with the promise of air strikes if it was broken.

Nato actions yesterday were thus aimed at propping this up, rather than at any longer-term political end. They were essential to underline the credibility of the UN position, alliance sources said.

Nato's last aerial attacks in Bosnia were around the besieged town of Gorazde in April. Then, there was confusion over UN and Nato communications, the political point behind the actions was uncertain and the Russians were furious. This time the rationale behind the attack was clear.

The move directly challenged Nato's promise in February that it would attack any heavy weapons in a 20km exclusion zone that were outside UN control. Coming at the same time as the Bosnian Serbs were threatening all-out war after they had rejected the latest peace plan, there was clearly a risk that such attempts could multiply.

Relations between the UN and Nato seem to be much better, and the Nato statement released after the attack emphasised that UN and alliance military officials had consulted closely on the decision. The UN yesterday also made a point of talking about consultation with Nato. Perhaps most importantly, the Russians are now tied into the peace process in Bosnia as members of the Contact Group, set up after the Gorazde fiasco, and have a broader political relationship with Nato.

As ever in the Bosnian conflict, however, the rationale behind any longer-term role for external force seems very hazy. Nato may be called upon for further such displays of force if the Bosnian Serbs continue to push their luck. But it is not at all certain that such one- off attacks can be used as a lever to press the Bosnian Serbs into peace. The situation is linked with the prospects for negotiations, with the Russian attitude and the mood of the countries providing troops for the UN presence in Bosnia.

If the military situation in Bosnia deteriorates rapidly, with further attacks on Unprofor personnel, then Nato has already prepared plans to assist the UN forces by toughening the policing of exclusion zones. But if it goes much further it may face resistance from the Russians, who have indicated they are not prepared to see Nato replace the UN in Bosnia.

Nor is it very clear what purpose such a strategy would serve in the longer term. Heavier fighting could well be the trigger for Britain, France and other troop contributors to withdraw, and Nato might be asked to assist in the removal of UN forces under fire.