The United Nations Security Council has unanimously approved keeping Nato troops in Macedonia to protect the international observers monitoring the next phase of a peace plan.

Earlier, Nato approved the force, to succeed the 4,500-strong British-led force which has been collecting weapons handed over by ethnic Albanian rebels.

The British-led force is preparing to move out on Thursday, once Nato's 30-day mandate for Operation Essential Harvest comes to an end.

On Wednesday, Nato ministers in Brussels agreed an operational plan for a new mission - to be called Operation Amber Fox.

Nato Secretary-General George Robertson said the force would be smaller than the current one and would be led by Germany.

The decision came after Nato officials and the Macedonian Government resolved a last-minute dispute over the size and duration of the force.

Protective mission

The troops' mission will change from collecting weapons to protecting about 120 civilian observers from the European Union and the Organisation for Security and Co-operation in Europe.

Albanians pledged 3,000 weapons

It is not clear what the extent of their mandate and the duration of their deployment might be.

Task force commander General Gunnar Lange said on Wednesday 3,875 weapons had been collected in the course of the Essential Harvest mission.

Ethnic Albanian rebels had pledged to hand over 3,000 weapons to Nato as part of a Western-backed peace plan signed in August, which aims to stave off the threat of a full-scale war in Macedonia.

Parliamentary process

As part of the deal, the Macedonian parliament is now supposed to approve changes to the constitution to give broader rights to the country's minority ethnic Albanian community.

Changes agreed

Drop reference to "national state of the Macedonian people" in preamble to constitution Allow use of Albanian language in state business Give ethnic Albanians jobs in public service and police in proportion to share of population

But the changes have only passed a preliminary hearing and it has so far failed to endorse an amnesty for most of the rebels.

Nationalists have tabled a proposal to put the amendments to a referendum, raising the danger of the whole process getting bogged down in delays.

"The political process is still incomplete, and the Macedonian parliament must set aside any petty political interest and complete its part of the settlement," said Lord Robertson.

"The world is watching and the politicians of this country know they have an obligation that they must fulfil," he said.

Even without a referendum, the changes to the constitution will require the approval of two-thirds of the parliamentary house.

Narrow votes in the initial stages of the parliamentary process suggest it will be hard to raise this level of support.