The crisis with Iraq is now entering its "final phase", the prime minister has told MPs.

Making a statement to the Commons on Monday, Tony Blair said the international community would be weakened if it failed to carry out its pledge to disarm Iraq of weapons of mass destruction.

Outlining the scale of his diplomatic efforts to secure agreement for a second United Nations security council resolution, Blair said that he had spoken to a number of world leaders, including those from Russia, Italy, France, Spain, Turkey, Poland, Canada, Greece and Australia.

"We are entering the final phase of a 12-year history of the disarmament of Iraq," he said.

Listing the series of opportunities Saddam Hussein had been given to meet his international obligations, the prime minister said time was running out for his "final chance" to comply.

"The evidence of cooperation withheld is unmistakeable," said Blair, pointing to chemical and biological weapons, missiles and documents that remain unaccounted for.

"There is a huge infrastructure of deception and concealment designed to prevent the inspectors from doing their job."

Blair also backed the United Nations process as the way to deal with the Iraqi leader.

And he warned that terrorist groups would be prepared to use the chemical or biological weapons that could be made available by Iraq.

"Unless we take a decisive stand now as an international community, it is only a matter of time before these threats come together.

"That means pursuing international terrorism across the world in all its forms. It means confronting nations defying the world over weapons of mass destruction.

"That is why a signal of weakness over Iraq is not only wrong in its own terms. Show weakness now and no one will ever believe us when we try to show strength in the future."

Failing to confront Iraq would not result in peace or security, the prime minister added.

"It will simply be returning to confront the issue again at a later time with the world less stable, the will of the international community less certain, and those repressive states or terrorist groups who would destroy our way of life emboldened and undeterred," he said.

If military force was used then the Iraqi people would be protected as far as possible and the territorial integrity of the country would be guaranteed, Blair pledged.

The Conservative leader backed the government, and warned that critics of tough action could shortly be facing a key choice.

"If and when a second resolution is secured, those who have to date opposed action to disarm Saddam Hussein have a stark choice. They can either back that second resolution and any military action that follows, or have the courage to admit that hey are opposed to military action in any circumstances," said Iain Duncan Smith.

"Saddam Hussein's day of reckoning is fast approaching. Peace or war, the choice is his - disarm or face the consequences."

But Liberal Democrat leader Charles Kennedy adopted a more sceptical tone.

He pointed to public anxiety and "the sense that an awful lot of people have right across the political spectrum...that we seem to be hastening into war ahead of events".

"The government have still to make a credible case and that case...has to be based on credible evidence and that evidence has not so far been forthcoming," he told MPs.

The statement came at the start of a week in which London and Washington will mount a propaganda and diplomatic offensive against the Iraqi regime.

Blair will this week use US intelligence about Saddam Hussein's weapons programme to seek further backing for military action.

The prime minister, who returned from his US trip over the weekend, has warned that Saddam poses a real risk to the West.

On Wednesday the US secretary of state, Colin Powell, will release transcripts of telephone conversations in which Iraqi officials boast about their success in hiding material from inspectors.

London and Washington will say the intelligence proves that Saddam's regime is deliberately concealing weapons of mass destruction.

Blair has won a six-week concession from president Bush - who is growing increasingly impatient with sceptical colleagues on the world stage.

The UN's chief weapons inspector returns to Baghdad on February 8 before filing his second report the following week.

Whilst London believes weapons inspectors must be given more time, it is warning that Baghdad is being offered its "last chance".