NOVI SAD, Yugoslavia -- Serbia's ruling Dos Alliance formally expelled the party of Yugoslav President Vojislav Kostunica on Friday, marking a final split among the reformers who ousted Slobodan Milosevic in 2000.

The decision to kick the Democratic Party of Serbia (DSS) out of the disparate 18-party grouping which had joined forces to topple Milosevic was in response to a court ruling in favor of Kostunica earlier in the day.

Kostunica is engaged in a bitter feud with Serbian Prime Minister Zoran Djindjic, the other main figure in the coalition.

Kostunica's party was elected on a DOS ticket but has since withdrawn from it in all but name, Reuters reported.

"(DOS) is excluding the Democratic Party of Serbia from the coalition," said Nenad Canak, leader of a junior coalition member after a meeting of its policy-setting body in the northern city of Novi Sad.

Djindjic and his allies in the DOS leadership moved last month to strip 21 deputies of Kostunica's party in the Serbian Parliament of their mandates as lawmakers, saying they had delayed reforms by failing to turn up for debates.

But on Friday the Yugoslav constitutional court upheld a complaint by Kostunica's party that DOS had no right to do that, and said the deputies could return to the benches.