Conference delegates have backed the TUC leader's warning that the UN is the "only possible route" to settling the crisis in Iraq.

John Monks opened the emergency debate at the TUC's Blackpool conference on Monday calling for "cast iron facts" supporting the case for military action.

His call was backed by conference delegates, who approved a statement by the TUC general council setting out their "unambiguous opposition" to unilateral military action.

A hard-line amendment by the Transport Salaried Staffs Association aimed at opposing military action was defeated by 3.4 million votes to 2.3 million after a card vote.

Monks warned that a unilateral strike would "spell disaster" for the Middle East.

He said the trade union movement wanted "every diplomatic solution" to be exhausted through the UN before war started.

"The UN is the only possible route to any action," Monks said.

He called on the prime minister to show "willingness to bring the country into its confidence" and bring forward clear evidence of the Iraqi dictator's weapons arsenal.

Monks warned there would be no support for Britain and America taking on Saddam on their own.

"We oppose any military action on a unilateral basis. That spells disaster," he said.

The TUC boss, who is seen as a key supporter of Tony Blair, said UN resolutions would also have to apply to America and Israel.

As a result of President Bush's decision to ignore the Kyoto agreements, Monks said British trade unionists were "rightly suspicious of unilateralist tendencies in the White House".

Monks was keen to show that the TUC were not appeasers of the Iraqi regime.

"No one in this room would have a good word to say about Saddam Hussein," he said arguing that the dictator had shown "a total disregard of human rights" and was a proven menace.

Monks argued that Tony Blair will have to say whether Saddam Hussein is really a threat to world peace.

Others offered a more hardline warning to Blair. Transport leader Bill Morris insisted that any action had to be backed by clear UN resolutions.

The clash came as TUC held an emergency debate on the growing threat of war with Iraq.

The debate, brought forward from its original Wednesday slot, came as Tony Blair prepared to call on unions to back his campaign against Saddam Hussein.

Number 10 has indicated that the prime minister will adopt a conciliatory tone when he addresses the conference on Tuesday.

"One of the things the prime minister will be talking about tomorrow in his speech at the TUC is that the UN can be a route to resolve this, but the UN has to deliver," said the Downing Street official spokesman.

"The UN is the embodiment of the international community, Saddam Hussein is a threat to the international community, he is in violation of UN resolutions, there is obviously an issue about how long the UN is prepared for its authority to be flouted.

"The prime minister will want to develop that in his speech."

With delegates approving the statement from union chiefs calling for a multilateral approach to the conflict, Blair may find it easier to reconcile his position with that of union members.

But suggestions that the UK and the US could press ahead with military action without a new UN resolution authorising the use of force are unlikely to go down well at the conference.