The opposition ultra-nationalist Serbian Radical Party (SRS) was trying to regain its footing on Monday following the resignation of second-in-command Tomislav Nikolic.

Nikolic, the acting chief of the SRS while leader Vojislav Seselj is on trial in The Hague for war crimes, resigned under pressure from hardliners displeased at his moves toward the political centre.

The resignation has raised speculation about a major rift in the party ahead of a vote on Serbia's relationship with the European Union (EU).

Nikolic was pushed out because of his intention to vote for the key Stabilization and Association Agreement (SAA) with the EU, widely seen as the first step on the road to membership of the 27-member bloc.

Nikolic also stepped down as SRS floor leader in parliament, a high-profile post representing the Radicals' 77 out of 250 deputies, retaining only his seat in the legislature.

The assembly is currently in an emergency session with several crucial items, including those paving the way to a pre-membership status with the EU, a big energy deal with Russia and loans worth a total of 400 million euros (570 million dollars), on the agenda.

Nikolic is credited with last week ending the Radicals' obstruction of parliament, which had already delayed ongoing debates by months.

The SAA vote is expected to take place later in the week.

Nikolic promised his party would back the SAA, while Seselj continues rejecting any approach to the West over its support of Kosovo's secession from Serbia in February.

Seselj is the cult leader of Serbian extreme nationalists, who has been in jail in The Hague facing charges of war crimes since February 2003.

Nikolic has recently revamped the SRS's image, turning it into Serbia's strongest single party.

The Radicals did not take part in the morning part of Monday's debate on financial arrangements, but huddled in a meeting instead, from which they emerged announcing a new floor leader, the hardliner Dragan Todorovic.

The daily Blic on Monday quoted sources as saying the SRS leadership would move to expel Nikolic from the party if he, as he promised last week, votes for the SAA.

"The key issue is whether Nikolic would try to tear the SRS or opt for something else, for a dignified silence or a quiet retirement," said political analyst Djordje Vukadinovic. "I think even he is not yet sure what to do and what is best for him."

Nikolic said he would decide on his future in the "coming few days," but hinted that he would not go quietly.

"A curtain is falling in front of the party - it may rise on two new parties or maybe one new party, but what SRS was has ceased to exist," he told Beta news agency.

For the time being, the victorious hardliners seem to be making an effort to sweep the mess under the carpet - new floor leader Todorovic said Monday his deputies would boycott the SAA vote.

Without a majority to stop the likely accession of the SAA, a boycott is perhaps as much to hide the SRS's divisions as to display their opposition.