Chancellor Gordon Brown says the UK "will spend what it takes" to tackle Iraq's weapons of mass destruction.
The UK denies Iraqi claims of bombing deaths
In casting aside his normal caution over open-ended spending, the chancellor has effectively offered a blank cheque for war against Iraq.
It comes as the Stop the War coalition unveiled plans for an anti-war rival to the House of Commons - a People's Assembly for Peace - to meet for a first time on 12 March in Westminster.
Organisers say it will give a voice to "the majority of people" across the country opposed to military action against Iraq.
Later on Tuesday Foreign Secretary Jack Straw is seeking to sell his hardline Iraq policy to Russian Foreign Minister Igor Ivanov during a meeting in Downing Street.
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Mr Brown told a meeting of business people in London: "I make no apology for saying we will spend what it takes to prevent the proliferation of chemical and biological weapons by states that defy international community and to advance the cause of disarmament.
"Our armed forces do an outstanding job for Britain and today I make clear our gratitude for the work they do and my resolve to ensure our armed forces are properly equipped for whatever lies ahead.
"The international community must not stand by whilst a regime that
proliferates weapons of mass destruction defies more than a decade's international agreements."
There is continuing speculation that Mr Brown may postpone his Budget until next month, because of the uncertainty over the Iraq crisis.
In November Mr Brown announced he was setting aside an extra £1bn to meet the costs of a new Gulf war.
Last month he promised an additional £750m.
The extra money referred to on Tuesday is unlikely to go down well with those many Labour MPs apposed to military action.
Meanwhile Mr Blair, currently in talks in Northern Ireland, has been hoping to join Mr Straw for the meeting with his Russian counterpart - a sign of the importance being attached to the discussions.
141,000 US troops in region
180,000 more US soldiers en route or on standby
30,000 UK troops in position
UK Tornado and Harrier aircraft deployed
Sixth US aircraft carrier group heading to Gulf
A Russian abstention in the vote on the US/UK second resolution would put more pressure on France as it decided whether to be the only permanent security council member to veto the resolution.
Critics of Mr Blair's Iraq policy unveiled plans for a national conference on 29 March for Labour members as they try to "reclaim" the party as an anti-war movement.
They want former Labour members to return to the fold through membership renewal forms stressing their anti-war credentials.
MP John McDonnell said: "If the leadership are not prepared to listen to the people of Britain in their clear opposition to this war, then the leadership will be swept aside."
The broader-based Stop the War coalition said the People's Assembly for Peace would give a voice to "the majority of people" across the country opposed to military action against Iraq.
Escalation not declaration
Downing Street disputed Iraqi claims of civilian casualties as a result of the action.
"We have conducted extensive battle damage assessment and we
can find no evidence to support Iraqi claims of civilian casualties," he said.
Anti-war Labour MPs suggested war was being started by "escalation not declaration" after senior Pentagon officials said no-fly zone patrols had become more aggressive.
On Tuesday, Conservative shadow defence secretary Bernard Jenkin accused ministers of being "deliberately obscure" about the changes.
Mr Jenkin urged the government to make a more comprehensive statement to Parliament.
On Monday, Mr Hoon insisted there had been no "substantial change" in the way the no-fly zones were patrolled.
Liberal Democrat defence spokesman Paul Keetch said Mr Hoon's denial of a change in patrols - despite the Pentagon briefings - raised suspicions.