Prime Minister Vojislav Kostunica told Serbs for the first time on Thursday the imminent loss of their historic province of Kosovo was a reality, but in a televised address he vowed the nation would never accept it.

Kostunica's statement was his most open acknowledgment yet that Serbia cannot prevent Kosovo's Albanian majority from proclaiming independence on Sunday, with the promise of Western recognition but without United Nations approval.

He said his coalition had adopted a document to pre-emptively annul "an event which will become reality in a few days, about illegal violence and an act of declaring independence of Kosovo".

"This decision confirms full national unity," Kostunica said, adding that what was about to happen was "a gross violation of international law".

At the United Nations in New York, Serbian Foreign Minister Vuk Jeremic told the U.N. Security Council on Thursday that Belgrade will use all its economic, political and diplomatic means to stop Kosovo seceding but will not resort to violence.

"We shall undertake all diplomatic, political, and economic measures designed to impede and reverse this direct and unprovoked attack on our sovereignty," Jeremic said in a text of his speech made available to media. He gave no details.

Serbia's state news agency Tanjug, in the first concrete report of diplomatic reprisals, said Serbia's ambassadors to France, Germany and Britain would leave in protest after they recognise Kosovo on Monday.

"Serbia has the right ... and Serbia will continue, through a series of concrete steps, to ... prove that Kosovo is part of Serbia," Kostunica told a news conference.

Radical Party deputy leader Tomislav Nikolic called on Kostunica and President Boris Tadic to organise a major protest rally against Kosovo's independence in the capital next week.

"If Sunday is a day of declaration of Kosovo's independence, the rally has to be held next week," Nikolic said.

He expected 1 million Serbs to turn out.

CALL TO EMBARGO TRADE

Kostunica said Serbia had demanded an emergency U.N. Security Council session on Thursday, and would ask Secretary General Ban Ki-moon to "take all steps and prevent the violation of the U.N. Charter, the Helsinki Act and Resolution 1244".

But Serbia's ally Russia has discounted the chances of the Council preventing Kosovo's proclamation of independence.

Russian President Vladimir Putin, however, said Moscow also had a plan ready in case the West recognised Kosovo's independence and would act to safeguard Russia's security.

Resolution 1244 was adopted in 1999 when NATO troops deployed into Kosovo after the Western alliance bombed Serbia to compel it to withdraw forces to end the killing and ethnic cleansing of Albanians in a counter-insurgency war.

Ninety percent of Kosovo's 2 million people are ethnic Albanians, but around 120,000 Serbs remain. An EU mission of some 2,000 police and judges will aim to ensure that promises of an equitable, multi-ethnic state under the rule of law are kept.

For Serbia, however, the mission will "not exist".

Kostunica, however, made clear that Serbia's cooperation with the NATO-led KFOR peacekeeping mission in Kosovo, which has a U.N. mandate, will continue.

BOSNIAN SERBS

Rumblings of potentially far more serious repercussions came from the Serb Republic, which makes up half of the state forged after the disastrous 1992-95 war, and now shares Bosnia with a Muslim-Croat Federation.

Serb nationalists stepped up their threats to secede from Bosnia, saying such a move could be launched even without a referendum "if the European Union recognises independent Kosovo unilaterally and against international law".

Bosnian Serb Prime Minister Milorad Dodik, who avoids direct threats of secession, said: "In case of a unilateral declaration of Kosovo independence, others can also develop such ideas".

A Western diplomat said: "It is difficult to discern the difference between the rhetoric and the probability", but he noted that Bosnia's Serbs were copying a legislative pattern Montenegro used in the run-up its independence two years ago.