The Yugoslav prime minister and his Montenegrin allies in the government have resigned and the Cabinet has collapsed after Mr Slobodan Milosevic's extradition.
The move by Mr Zoran Zizic and other former Milosevic's allies is expected to lead to early federal elections.
Meanwhile, an official says Serbia's president, who wasindicted along with Milosevic by the UN war crimes tribunal,may surrender to the court.
Mr Milan Milutinovic is "considering" giving himself up now that Mr Milosevic is in The Hague to face trial on charges of crimes against humanity, an Interior Ministry official has stated.
It is not immediately clear whether Mr Milutinovic will offer to testify against Mr Milosevic. Both men face charges in connection with alleged atrocities committed by Serb troops in Kosovo against ethnic Albanians during the 1998-99 war in the Yugoslav province.
Commentators say the resignations from the government mayeven hasten a split between Serbia and much smallerMontenegro in the existing Yugoslav federation.
The federal government is made up of Serbia's pro-democracyofficials and ministers from Montenegro who turned their backs on Mr Milosevic after he was ousted.
The Montenegrin officials, who met in the republic's capitalPodgorica, said in a statement that Mr Milosevic's extradition to The Hague-based tribunal was "illegal and unconstitutional."
They said it "jeopardizes the functioning of Yugoslavia and its existence"
The fromer president was handed over to The Hague tribunal yesterday by the Serbian government, which ignored a federalConstitutional Court ruling that banned his extradition.
In a separate move, President Vojislav Kostunica's party, angry at the transfer of Mr Milosevic to the UN war crimes tribunal, decided today to leave the parliamentary groups of the ruling DOS reformist alliance.
The Democratic Party of Serbia (DOS) said it would leaveboth the Serbian and federal parliaments and also wanted a reshuffle of governments on both levels.
But party leaders said this did not mean they were leaving completely the 18-party DOS, which united to oust Mr Milosevic in a mass uprising last October.
They said they had made their decisions partly because of a Serbian government decision yesterday to hand over the former president. Mr Kostunica criticised the move as illegal and unconstitutional.
"This is not just about the illegal extradition of the former Yugoslav president but also about many previous moves which were in complete disaccord with the basic constitutional order and the coalition's objectives," a party statement said.
PA