Russia has said it will vote against a draft resolution proposed by the US and UK that gives Iraq a 17 March deadline to disarm.
Iraq is gearing up for conflict
It is the first time that Russia has explicitly said it will veto the resolution if it is presented to the UN Security Council in its current form.
France, another permanent member, has said it will not let a resolution pass that authorises the automatic use of force, while China has also indicated its opposition to military action at this point.
And in another blow to the US and UK, the UN Secretary-General, Kofi Annan, has spoken out against any military action against Iraq that lacks the support of the Security Council.
The members of the Security Council faced a grim task, Mr Annan said.
"If they fail to agree on a common position and action is taken without the authority of the Security Council, the legitimacy and support for any such action would be seriously impaired," he said.
Hours earlier, Russian Foreign Minister Igor Ivanov said the draft resolution was impossible to fulfil and ran counter to the policy currently being implemented under resolution 1441.
The White House said it hoped Russia and France would not veto a second UN resolution on Iraq.
"If they were to veto...it would be, from a moral point, more than a disappointment. It would let down millions of people around the world, in this case Iraq, who deserve to be free and have a better life," White House spokesman Ari Fleischer said.
In other developments:
Diplomats are gathering shortly (at 2100G) to resume consultations on the second UN resolution.
- Iraqi forces are reported to have placed explosives around the oil fields in the Kirkuk region in northern Iraq, according to US officials
- Iraq is determined to fight "until the
end" and will not surrender, Iraq's Deputy Prime Minister Tariq Aziz tells reporters in Baghdad.
- US and British warplanes patrolling southern Iraq on Monday attacked air
defence targets in the "no-fly" zone for the fourth consecutive day, the US military says
- Britain's International Development Secretary Clare Short warns she will resign if Britain joins an attack on Iraq without UN approval
But despite intensive lobbying over the weekend, it is by no means certain that Britain, the United States, and Spain, which is also promoting the resolution, have the support they require to see it passed.
Our world affairs correspondent Paul Reynolds says the best that Mr Bush and Mr Blair can hope for if there is a veto is to get the so-called "moral majority".
This would be nine of the 15 Security Council votes, but a "moral majority" has no legal status.
President Bush has been making an urgent round of calls to world leaders, including Japanese Prime Minister Junichiro Koizumi and China's President Jiang Zemin.
But French Foreign Minister Dominique de Villepin has also been touring the three African members of the Security Council - Angola, Cameroon and Guinea, to try to persuade them to reject the resolution.
After talks in Luanda, Angolan Foreign Minister Joao Bernardo de Miranda, told reporters that Angola was not prepared to commit itself until it came to a Council vote.
Mr de Villepin told the same news conference that a solution to the crisis in Iraq could be found without resorting to the use of force.
As the diplomatic tempo increases, reports from Islamabad suggest Pakistan, a non-permanent Security Council member, has decided to abstain in any vote that will allow military action against Iraq.
Giving the weapons inspectors more time, as proposed by France and Russia, would "amount to the failed policy of so-called containment," UK Foreign Secretary Jack Straw has said.
Iraq was not being asked to disarm within a week, Mr Straw said in parliament in London.
"But what we are expecting is that the Iraqi regime should demonstrate the full, unconditional, immediate cooperation demanded by successive resolutions since 1991," he said.
To that end, Mr Straw said the UK Government wanted to draw up a list of tasks for Iraq to show it was serious about disarming.
The detailed disarmament moves are likely to be drawn from a document compiled by UN chief weapons inspector Hans Blix which says Iraq has not fully disposed of its chemical and biological weapons arsenal.
It is now expected that the new resolution will not be put to the vote until Wednesday at the earliest.