Croats seek Nato patrol on their Bosnian border

US and European diplomats are considering a Croatian proposal for a new Nato or European multinational force, not under United Nations command, to maintain an international peace-keeping presence in Croatia when the UN mandate expires on 31 March.

But as it stands, the plan for a 5,000 to 6,000-strong force - one-third of the size of the present UN force - along the Croatian border with Bosnia suits only the Croats. The Foreign Office said yesterday that the idea was a non-starter. "We want Unprofor [the UN Protection Force] to stay. We are not contemplating an alternative."

The British, French, German and US defence ministers, meeting in Fort Stewart, Georgia, yesterday, warned that a UN pullout from Croatia could spark a war that would engulf the entire region. "We would quickly see the collapse of the current fragile ceasefire and the resumption of bitter fighting which would bring great loss of life," the Defence Secretary, Malcolm Rifkind, said.

UN sources in Zagreb take the plan for a Nato force seriously, however. After the collapse of the five-nation Contact Group initiative on Thursday night, members, including the US Assistant Secretary of State, Richard Holbrooke, are expected in Zagreb on Monday for discussion with President Franjo Tudjman on deploying the new force.

It would report to Nato, the European Union or the Organisation for Security and Co- operation in Europe (OSCE).

On Tuesday the departing UN commander in all former Yugoslavia, General Bertrand de Lapresle, said he thought the UN would remain after 1 April, but in a different form and under a new mandate. However, the Croatian government then issued a public statement saying continuation of the mandate was out of the question.

The Croats want the force to be deployed along the Croatian-Bosnian border, where it will not get in the way of operations they appear to be planning against the Krajina Serbs in Croatia. The UN polices the "zone of separation" between Krajina and the rest of Croatia.

The proposed arrangement would not protect the Krajina Serbs but would get in the way of aid coming from the Bosnian Serbs across the border. The Croatians see advantages in getting Nato, the EU or the OSCE to guard their border against incursions by Bosnian Serbs.

The structure of the UN forces in former Yugoslavia is expected to alter radically after the UN withdrawal begins. There are two UN forces: Unprofor 1, 15,480-strong, in Croatia, and Unprofor 2, which is 23,600-strong, in Bosnia, though it has bases on the Croatian coast .

If Unprofor 1 goes, the top-level UN headquarters in Zagreb looks unlikely to remain, with some command functions passing down to Sarajevo in Bosnia and others pulled back to a new UN headquarters at Ancona or Brindisi in Italy or possibly Skopje in Macedonia.

Unprofor 2 will be allowed to keep its bases at Split and Ploce on the Croatian coast, but the Croats may use those bases as levers to extract more money from the UN. UN bases at Zagreb, Ploce and Split are worth $250m (£158m) a year to Croatia's economy.