Leading Article: No choice now but to act

ADECISIVE moment has been reached. Once again the Bosnian Serbs have called the bluff of international opinion. Despite overwhelming pressure to accept the Vance-Owen peace plan signed on Sunday by their own leader, Radovan Karadzic (and to which at one stage of the night they seemed to have succumbed), they eventually rejected it by an overwhelming majority. The challenge to the United Nations as a whole and to Nato in particular to take firm action to stop the slaughter and ethnic cleansing has thus been posed with renewed urgency.

All that has been gained in the past few days is an open rift between the Serbian leader, Slobodan Milosevic, on whose rump Yugoslavia UN sanctions are now biting hard, and the so-called Bosnian Serb parliament. That must clearly be exploited to the full: Lord Owen yesterday seemed to regard it as the best chance of bringing the Bosnian Serbs to their senses. Mr Milosevic now seems to have decided to seal the Serbian and Montenegrin borders with Bosnia, cutting off vital supplies of fuel and arms to the militias. But Serbs of the Yugoslav army may not enforce such orders against their kinsmen in Bosnia with uniform zeal.

Certainly the buck cannot be passed to Mr Milosevic, whose ruthlessly opportunistic appeals to Serbian nationalism triggered the original break-up of Yugoslavia. So both for the UN and Nato there now seems no choice but to take some form of action that will halt the civil war and enable the Vance-Owen plan, or something similar, to be implemented. The possible alternatives are numerous. One is the creation of some form of safe haven for civilians, and especially for Muslims. Such areas could be declared no-go zones for Bosnian troops of whatever ethnic persuasion, with punitive action promised against military intruders. Whether such havens could be effectively guaranteed from the air alone is doubtful. Experience in southern Iraq, where President Saddam Hussein's persecution of the marsh Arabs continues, suggests otherwise.

Another, or parallel, option is to beef up and give a freer hand to the UN troops already escorting convoys of humanitarian aid. Their task could be extended to the defence of threatened communities, and they could be supported by helicopter gunships and mobile artillery. American involvement, hitherto promised only for the policing of an accepted peace plan, would be required to give such a mission full credibility. US experience in Somalia suggests it could be very effective. A third option would be to bomb Bosnian Serb supply lines, depots and artillery. A fourth - arming the Muslims - is still regarded by the Europeans, probably correctly, as a recipe for fanning the flames of war.

While contingency planning continued, yesterday's consultations in Brussels did nothing to correct the dismal impression of continuing allied vacillation and disagreement. Americans and Europeans should now be facing up to the likelihood that peace will have to be imposed before it can be kept. Governments should begin to prepare public opinion for such a switch, and the military must establish how it can be achieved with the least loss of life.