Nato sources say about 2,000 additional personnel and new military equipment have been sent to Kosovo, and the Yugoslav Army has stationed an armoured brigade nearby.

The American Secretary of State, Madeleine Albright, warned Yugoslav President Slobodan Milosevic on Wednesday that a new offensive would be a grave mistake.

The Serbian authorities have denied suggestions they are planning a new offensive.

Jonathan Marcus: "The KLA incident could be a protest to strike"

BBC Defence Correspondent Jonathan Marcus says any significant Yugoslav military action before peace talks resume in mid-March would present Nato with a serious dilemma.

Alarmed by reports of a possible new Serbian offensive, Albanian Premier Pandeli Majko reiterated his call for Nato to intervene on the ground.

"Belgrade is sending troops massively into the region (of Kosovo) in what I see as a preparation for a general offensive against Kosovo," he said in a letter sent to Nato Secretary-General Javier Solana.

He said Nato is the only institution capable of forcing Belgrade to stop the violence.

KLA delegates return home to criticism

Peter Biles reports for BBC World

The latest concern coincides with the return of the delegation of ethnic Albanians from Kosovo, who finally made it home from the peace talks in France.

The Albanians were forced to postpone their journey by a day because the Serbian authorities initially refused to provide guarantees of safe passage through the airport of Pristina for those in the delegation who are members of the KLA.

The negotiators have also announced plans to form a transitional ethnic-Albanian government as required by international mediators, despite reports that they were divided over the issue.

But the KLA's political chief Adem Demaci - who did not go to France for the peace talks - warned such a government would have no legitimacy.

"The KLA and its political representative have not been consulted on the formation of a so-called provisional government," Mr Demaci said.

Mr Demaci's criticism followed reports on Wednesday that the three senior members of the Kosovar Albanian delegation at the Rambouillet peace talks, including the KLA team's leader, Hashim Thachi, had agreed to set up a government which would be headed by a politician to be nominated by the KLA.

Shelling accusations

Fighting is meanwhile reported to have continued in Kosovo, with the ethnic-Albanians accusing Serbian forces of shelling villages in the northern Podujevo area.

There was also a tense stand-off between the Serbian security forces and units of the KLA near the southern town of Suva Reka.

The KLA were refusing to allow a Serbian patrol along a road surrounded by KLA territory. The OSCE's monitoring mission was there in force trying to keep the peace. A senior KLA zone commander said he thought the Serbs were trying to provoke the KLA in order to mount a new offensive.

The returned ethnic Albanian delegation is about to embark upon a two-week consultation period before a decision is taken on whether to sign the interim peace agreement. Ethnic Albanians of Kosovo make up 90% of the population of the province.