A confident Croatia advances its cause: Steve Crawshaw, East Europe Editor, examines Zagreb's military progress and the new fears it has raised among Muslims in Bosnia

THE RELIEF of Sarajevo may at last be within sight, now that the West has begun to take concerted action in order to break the Serbian siege of the city. But the Serbs are not the only ones who are capable of creating lethal problems in what was Yugoslavia. Now the Croats are growing in confidence - and are, perhaps, almost equally dangerous to Bosnia-Herzegovina, in the longer term.

Apparently in response to the newly tough Western stance - including the threat of direct action in Sarajevo, which was previously excluded - Radovan Karadzic, the Serbian leader in Bosnia, has started talking peace for the first time (although he also said yesterday that Serbs would have 'no choice but to fight', if US forces sought to disarm Serbs who have been besieging Sarajevo). So far, so good.

But the violence may move on. The Croats - who have been at the receiving end of most of the violence in the past year, when Serbian forces and the Yugoslav army shelled Croatian cities into annihilation - are more bullish than ever before.

In Croatia itself, the Croats have made notable military advances in recent days and weeks, seizing the advantage while they can. Large areas in the Serbian-majority region of Knin - where rebellion against Croatian rule began in August 1990 - have been seized, and at least 100 people have died.

The United Nations, dismayed that the Croats have ignored the writ of the peacekeeping force, has called for President Franjo Tudjman's government to pull back. A UN Security Council resolution this week talked of 'grave consequences' for the region, if the international peacekeeping effort collapses.

But neither Serbs nor Croats are much interested in compromise. Mr Tudjman's early intolerance towards Croatia's large Serbian population, after his election in 1990, contributed towards inflaming Serb-Croat relations; the Serbs, in turn, have shown themselves ready to use unlimited violence against the Croats. The UN peacekeepers, as far as both sides are concerned, are merely an irritating interruption of unfinished business.

In some areas, the Serbian violence has not ceased: for example, at least four people have died in recent days in the renewed shelling of Dubrovnik. Attacks on the city continued yesterday.

Elsewhere, however, Serbia is retreating, for the first time. In Bosnia, the Croats have been understandably keen to advance. Theoretically, that should be to the advantage of the Slav Muslims, the largest single ethnic group in Bosnia-Herzegovina, who have had a semi-alliance with the Croats. But Muslims are nervous of the Croats' strength - especially in view of Serb-Croat talks in recent months about a possible carve-up of the Bosnian republic, which would squeeze out the Muslims altogether.

Large parts of western Herzegovina are ethnically Croatian, and Mr Tudjman has in the past talked about Croatia 'within its historic borders' - that is, including chunks of Bosnia. Mr Tudjman has done nothing to dissuade Croats in Bosnia from declaring their first loyalty to be to Zagreb, not to Sarajevo. In western Herzegovina, Croatia's red-and-white checkerboard symbol is used, rather than the Bosnian fleur-de-lis. Even the Croatian currency is used.

There has been Croatian violence against Muslims, too. In Novi Travnik, west of Sarajevo, Croats last month attacked Muslims, and killed four. Elsewhere, Serbs and Croats have formed what some Muslims regard as an unholy alliance. A Reuter correspondent west of Sarajevo described how the Croatian commander in the Croatian- held town of Kiseljak, and his Serbian counterpart in nearby Ilidza, both talked of each other as 'partners' and 'friends', who visited each other regularly. The Serbian commander in Ilidza said the Serbs and Croats had 'identical interests'.

For the Bosnian Muslims, the Croatian military victories - which the West has welcomed, not least because it obviates the need for the West to intervene - may come to seem an unwelcome gift, if the Serbian destruction of recent weeks is followed by an insistence that 'Croatia the Liberator' will now call the shots.

All hopes of Bosnian Muslims - and of non-nationalist Bosnian Serbs and Croats - for mutual tolerance may then be difficult to sustain.

(Photograph omitted)