Nato wonders which targets to hit next

Nato air attacks on the Bosnian Serbs intensified yesterday with the heaviest bombing yet against ammunition dumps around Sarajevo. Nato said they will go on until the Serbs withdraw all their heavy weapons from within a 20km radius of the city centre.

There was, however, confusion about what targets to hit next as Nato nears the end of its original list, now expanded to about 150 "aiming points".

Nato denied a report that its Secretary General, Willy Claes, had said he wanted to shift attacks from rear-area targets - ammunition dumps, command control and communications - to Bosnian Serb front-line troops. And the UN special representative, Yasushi Akashi, said he was reluctant to shift the focus in the opposite direction, to "option three": attacks on industrial infrastructure.

Despite criticism from Moscow and the risk that the continuing raids will upset wider peace negotiations, the UN and Nato are standing by their threat to tear the military structure apart until the Bosnian Serbs do as they have been asked.

For the moment, there are still enough targets. The highest priority are air defences like those attacked with cruise missiles on Sunday. Although the integrated air defence system has been severely damaged, military sources said there are still areas which are regarded as unsafe for Nato aircraft. Therefore, there may be further attacks, possibly using cruise missiles or, once Italian sensitivities are overcome, F-117 Stealth fighters which can evade radar, infra-red and electromagnetic detection, until Nato can use the skies unchallenged.

The 150 targets on the present Nato list were selected from thousands, most of which had to be discarded because they were too close to civilian areas. Nato is acutely conscious that a single bad error, leading to large numbers of civilian deaths, could turn world opinion against operation "Deliberate Force".

Nato's concern to avoid "collateral damage" is one reason why the air campaign is proceeding slowly. The Nato aircraft are using a high proportion of laser-guided bombs, which are delivered a few at a time, rather than deluging the targets with "dumb bombs". This has meant the campaign has taken longer. Whenever aircraft cannot find the target, or whenever bad weather intervenes, its progress is further delayed.

However, it takes time for the effect of destroying ammunition dumps to filter down to artillery positions. By the standards of conventional war, the ammunition expenditure in the Bosnian conflict is modest. The Serbs are believed to have about 300 guns around Sarajevo, all of which are believed to have three weeks' supply of ammunition to hand. Only when those stocks are used up will the destruction of ammunition depots begin to tell at the front.

But some military sources are slightly concerned that the Bosnian Serbs may prove more resilient than expected. "It's the world's biggest underground army," said one UN official. Tito's Yugoslavia was honeycombed with underground installations to enable it to withstand a nuclear attack or Soviet invasion. The Bosnian government believes Nato may have hit about 100 "heavy weapons" - tanks guns and mortars - out of an estimated Bosnian Serb strength of about 2,000, but Nato and the UN refused to make any estimate.

Still more uncertain is the effect on the will of the Bosnian Serbs who were believed to be overstretched and war-weary. It is possible, however, that the Nato bombing could stiffen rather than weaken their resolve. That has been the effect of previous bombing campaigns in Europe and Asia.