Ultranationalist Tomislav Nikolic stepped down Sunday, after serving as speaker only for five days, the Serbian news agency Beta reported Monday.

Nikolic quit his post under pressure from Serbian pro-Western and reformist politicians, supported by the United States and the European Union, who warned the international community would not welcome an anti-European government.

On his election Tuesday, Nikolic said his Radical party would oppose ties with the EU and NATO and instead would develop close ties with Russia.

On Friday, the Democratic Party of Serbia of conservative Serbian Prime Minister Vojislav Kostunica renounced its support of Nikolic's radicals and reportedly agreed with the Democratic Party of Serbian President Boris Tadic to forge a coalition of more than 126 lawmakers in the 250-seat parliament.

The parliament's majority is to approve a new coalition government, to be led by Kostunica, by midnight Tuesday. Serbian parties have tried to agree on a coalition since parliamentary elections on Jan. 21 that produced no clear-cut winner.