Tony Blair, President Bush and Spanish prime minister Aznar will meet in the Azores on Sunday for an emergency summit on Iraq.

The mid-Atlantic islands will host the three key pro-war allies' discussions on whether to go war without a second United Nations resolution.

The White House confirmed that the meeting would take place as part of their "fluid and dynamic" diplomatic efforts to secure international support for the forceful disarmament of Saddam Hussein.

With French support still the main stumbling block to a second UN vote, Blair has urged president Chirac to back military action if Saddam fails to disarm voluntarily.

The British and French leaders held what was described as a frank but good-natured telephone call on Friday.

Number 10 said that during the conversation, held at France's request, there was no sign of France backing down on its pledge to veto any move to authorise the use of military force.

"President Chirac said he was willing to look at the tests the UK had put down in the United Nations but insisted there were no circumstances in which France would countenance any UN resolution which authorised or implied military action should the tests not be met," said the prime minister's official spokesman.

"And he said he would not accept an ultimatum to Saddam. The prime minister said that without a credible threat that military action would be used to enforce the will of the United Nations, there would never be the necessary pressure on Saddam to disarm."

The latest negotiations came amid speculation that the leaders of Britain, America and Spain would hold a crisis summit this weekend.

If they conclude that no progress is being made at the United Nations in New York, they could decide on alternative strategies for pushing ahead with the use of military force to disarm Iraq.

Downing Street confirmed the prime minister is considering a three-way meeting.

Washington officials have also confirmed the idea is being reviewed and that the meeting would be held in a neutral country if it went ahead.

There have been further signs that the diplomatic effort to gain support for the second resolution is still facing major problems after Germany said it was still unconvinced of the need for war.German chancellor Gerhard Schroeder said: "We must have the courage to fight for peace as long as there is a scrap of hope that a war can be avoided.

"Together with our French friends, with Russia and China, we are more than ever convinced that Iraq's disarmament can and must be achieved by peaceful means.''

Despite the continuing problems, frantic discussions are to continue at the UN.

Washington has said it is prepared to grant a little more time for discussions on a new resolution, but has repeated that this is the "very last stages of diplomacy".

"The president is willing to go the extra mile for diplomacy," said White House spokesman Ari Fleischer.