Robert Parsons reports from Moscow

The provisional agreement - struck between the lower house of parliament, the Duma, and Mr Chernomyrdin - is is set to involve constitutional changes to strip President Boris Yeltsin of some of his key powers and to transfer them to parliament.

Russia analyst Alexander Konovalev on the Communists' tactics

However, a group of parties, who together hold 228 of the 450 seats in the Duma, say they will vote against confirming Mr Chernomyrdin as prime minister later today.

Mr Chernomyrdin is currently meeting opposition politicians in a final bid to change their minds before the vote.

The group - which includes the largest faction in the Duma, the Communists - could deny Mr Chernomyrdin the simple majority he needs for his candidacy to be successful.

Opponents lining up

In a television interview, the Communist leader, Gennady Zyuganov, described Mr Chernomyrdin as "an accomplice in the destruction [of the country]".

Zhirinovsky: angling for cabinet posts

He also appeared to reject the power-sharing deal, saying it did "not guarantee anything to anyone".

The extreme-nationalist leader Vladimir Zhirinovsky, whose Liberal Democratic Party is the third largest Duma faction, also said he would vote against Mr Chernomyrdin's candidacy unless his party was offered several cabinet posts.

The pro-market reform Yabloko faction,

Deal follows talks between Mr Chernomyrdin and Duma

which has been consistently critical of Mr Yeltsin, also said it would not support Mr Chernomyrdin.

One of the BBC's correspondents in Moscow, Paul Anderson, says the Communists' threat to vote against Mr Chernomyrdin may well be a bargaining ploy in order to win more concessions in the power-sharing deal.

BBC Moscow Correspondent Paul Anderson: Communists may be pushing for concessions

In particular, Mr Zyuganov has demanded changes to the terms of Russian loan payments to the International Monetary Fund (IMF).

Our correspondent says that Mr Chernomyrdin's chances of being confirmed are not necessarily over.

Many Communists have defied their leaders' demands in similar past votes in the Duma.

Yeltsin yet to agree deal

However, even if he is confirmed, Mr Chernomyrdin may find his woes are not over yet.

Mr Yeltsin, is due to deliver his formal response to the power-sharing agreement later today.

Yeltsin may be reduced to a figurehead

He has already signalled his disquiet with the document and its provision for him to cede some powers to the Duma.

In a television interview, the beleaguered president said he believed it was premature to talk about constitutional amendments to transfer those powers.

He said they could be considered, but only through a commission that might take a year to complete its work.

G7 nations pledge support for reform

As the political bargaining in Moscow has continued, the US President Bill Clinton - who is due to arrive in Moscow on Tuesday - has repeatedly called for Russia to continue to pursue the path of market reforms begun by Mr Yeltsin.

Clinton: mission to Moscow

On Sunday he had a telephone conversation about the crisis with the UK Prime Minister, Tony Blair.

Mr Blair, in his role as the current Chairman of the G7 also consulted the other leaders of the group of major industrial nations about the situation.