"Don't look beyond March" says the UK ambassador
The United States has flatly rejected calls to extend a deadline for Iraq to disarm by up to 45 days.
A draft resolution that the US and Britain are planning to bring before the divided United Nations Security Council says that Iraq should be given until 17 March to give up banned weapons - or face military action from US-led forces.
British diplomats have been seeking possible amendments to the text, to avoid what BBC correspondents say looks like an inevitable defeat in the 15-member body.
Russia and France have made it clear that they will use their powers of veto against any resolution that gives the green light for war.
A suggestion by the six undecided, non-permanent members of the Security Council that the deadline be extended into April or beyond was described as a non-starter by the US administration.
Deadline, possibly 10 days, for Iraq to make strategic decision to disarm
17 March deadline to be postponed
Destruction of banned weapons
Evidence of previous claims of destroyed weapons
Interviews with Iraqi scientists abroad
"There's room for a little more diplomacy here but not much room and not much time," said White House spokesman Ari Fleischer.
Amid signs that the Americans are growing increasingly frustrated with the UN route, he insisted that a vote on a new resolution would take place this week.
At the UN, Iraq's ambassador Mohammed al-Douri, urged the international community to prevent "a catastrophe which has become imminent".
Mr al-Douri was speaking on the first day of a two-day open session called by non-aligned states to discuss the draft resolution.
The majority of the 28 speakers who addressed the council called for a peaceful solution to the crisis.
Canada, which has been influential over undecided council members, called for a three-week deadline for Iraq to demonstrate it had fully complied with the UN's disarmament demands.
The debate has been adjourned until 1500 local time (2000 GMT) on Wednesday.
The Americans and British have said they are prepared to go ahead with a military assault on Iraq without the backing of a new resolution.
There is some suggestion that if the nine votes required to pass the resolution are mustered before it is vetoed, then the Anglo-American side would claim this as a "moral victory".
The US and Britain have built up a massive military presence in the Gulf region.
BBC defence correspondent Jonathan Marcus says American and British planes patrolling longstanding "no-fly zones" over Iraq are stepping up raids on air defences in the country to weaken them ahead of a wider conflict.
And the US army says earth fortifications along the Iraq-Kuwait border are being removed to allow an overland assault to begin.
Meanwhile, the US and Turkey are holding talks about the use of Turkish airspace by American forces in the event of war.
Plans to allow US troops into Turkey, enabling the opening of a northern front in any attack on Iraq, have been blocked by the country's parliament, but that decision may yet be reversed.
In other developments:
US Defence Secretary Donald Rumsfeld qualifies remarks suggesting US forces might act without British military support, saying the US had "every reason to believe there will be a significant military contribution from the United Kingdom".
- The US military says it has successfully tested a massive 21,000 pound bomb - known as the Moab: Massive Ordnance Air Burst or, unofficially, the Mother Of All Bombs - which may be used in any conflict with Iraq
- UN inspectors' spokesman Hiro Ueki says Iraq has destroyed three more of their banned al-Samoud II missiles, bringing the total destroyed to 55 out of about 100
- Mr Ueki says three pilotless drones, which the US says can deliver weapons of mass destruction, have been discovered
- Two American U-2 spy planes supporting UN inspections are withdrawn from Iraqi airspace after Baghdad complains they flew in from Saudi Arabia, breaching an agreement with inspectors