The Iraq stand-off is entering its final stage, UK Foreign Secretary Jack Straw has said as he promised MPs a full debate on the crisis.
Troops in the Gulf are ready for war, the US says
Mr Straw's speech came as Prime Minister Tony Blair met his Italian counterpart, Silvio Berlusconi, to discuss possible military action against Iraqi leader Saddam Hussein.
The UK premier is to have a private audience with the Pope while he is in Rome and on Friday set out against the "moral dimension" to his tough stance.
Religious leaders have voiced their doubts about possible war, but in London Mr Straw said disarming Saddam Hussein had "compelling moral force".
Mr Straw said: "The United Nations has been trying to remove a central pillar of Saddam's apparatus of terror - his weapons of mass destruction - for the past 12 years.
"As this stand-off enters its final phase, my message today is that in securing Iraq's disarmament we will remove the threat Saddam poses to his neighbours and the wide world.
"We will also effect a decisive shift in the fortunes of the long suffering Iraqi people, and we will have reasserted the authority of the international rule of law."
Mr Straw said the prime minister would make a Commons statement on Tuesday about this week's emergency European Union summit about Iraq.
The next day both Houses of Parliament would debate a "substantive motion" about the crisis.
Mr Straw added: "Of course, no such national debate would be possible in Iraq. Saddam has no marchers to persuade of his murderous policies."
Unless other means have been really exhausted, it's very hard to justify military action, and certainly pre-emptive action
Archbishop of Canterbury
The wording of the motion is not yet known, but anti-war MPs have said any military action must be specifically authorised by a vote of Parliament.
Ahead of his audience with the Pope John Paul II, Mr Blair said he shared the dislike of war voiced by church leaders.
But a peaceful solution to the crisis could only happen if Saddam Hussein chose to disarm.
"We do not want war. No one wants war. The reason why last summer instead of starting war, we went to the United Nations was in order to have a peaceful solution to this," he said during a press conference with Mr Berlusconi.
"But there is a moral dimension to this question too.
"If we fail to disarm Saddam peacefully then where does that leave the authority of the United Nations?
"And if we leave Saddam in charge of Iraq with his weapons of mass destruction, where does that leave the Iraqi people who are the victims of Saddam?"
American and British diplomats are drawing up a second resolution to present to the UN security council but Mr Blair refused to say when that would be published.
Mr Straw dampened expectations for a dramatically stronger resolution, saying the wording of the last resolution clearly threatened disarmament by force.
That did not satisfy Liberal Democrat foreign affairs spokesman Menzies Campbell, who said any military action had to be authorised explicity in a new resolution.
There is opposition to Washington's approach from some European leaders, with France and Germany still against military action.
Speculation about military action has been fuelled by US Defense Secretary Donald Rumsfeld's assertion that American and British troops are now ready for war.
Mr Berlusconi's government has been supportive of the President George W Bush's stance.
Anglican and Catholic archbishops have raised their doubts
But there have also been signs that Mr Berlusconi's four-party coalition is heeding public disquiet over possible war, saying it wants a second UN resolution to authorise any use of force.
Italy has not sent troops to Iraq but is offering the US staging facilities and overflying rights in the event of an invasion of Iraq.
Mr Blair will meet the Pope, who has voiced his anxiety about possible war with Iraq, on Saturday.
On Friday, Archbishop of Canterbury Rowan Williams again stressed war could only be a last resort in self-defence.
"Christians generally would hold through the ages that unless other means of resolution have been really exhausted, it's very hard to justify military action, and certainly pre-emptive action," said Dr Williams.