Tony Blair warned yesterday that the UN only had a matter of weeks to establish that Iraq had rid itself of weapons of mass destruction.

The Prime Minister signalled that today's report from the inspection teams' leaders to the UN Security Council would not mark the end of their efforts - but emphasised that their mission in Iraq could not be open-ended.

US Secretary of State Colin Powell, in a speech to the World Economic Forum in Davos, Switzerland, sent a similar message.

He warned Iraqi dictator Saddam Hussein that while the US would not rush to judgement on the basis of today's report, nevertheless "time is running out".

At today's Security Council session in New York, the UN's chief weapons inspector Hans Blix, and International Atomic Energy Agency (IAEA) chief Mohamed ElBaradei will report on progress in their two-month-old hunt for Baghdad's alleged weapons of mass destruction.

The IAEA said yesterday that it would tell the Security Council that it has yet to prove that Iraq is secretly seeking atomic weapons.

However, Mr ElBaradei will say that he cannot report positive progress on the key issue of private interviews with Iraqi scientists.

Mr Blix, whose inspectors are checking for any banned chemical, biological and ballistic weapons, is expected to be more critical than Mr ElBaradei, telling the council that Baghdad left large gaps in the arms declaration it supplied on December 7 as well as blocking interviews with scientists.

Both are expected to say that they need more time.

Interviewed on BBC 1's Breakfast with Frost yesterday, Mr Blair said they should have some leeway.

"The job of the inspectors is to certify whether Saddam is co-operating or not with the UN inspections," he said. "That duty to co-operate doesn't just mean that he has to give them access to particular sites.

"It means he has got to co-operate fully in saying exactly what weapons material he has, allowing the inspectors to inspect it, monitor it and shut it down."

Asked whether the timescale should be weeks or months, Mr Blair said: "I don't believe it will take them months to find out whether he is co-operating or not, but they should have whatever time they need."

Mr Blair warned that a failure by Saddam to co-operate with inspectors amounted to a breach of UN resolutions "that is every bit as much a breach as finding, for example, a missile or a chemical agent".

The Prime Minister insisted that the Government was "very focused" on getting a new UN resolution over and above resolution 1441 - which gave the inspectors their mandate - before taking any military action.

The only way war would take place without a second UN mandate was if the weapons inspectors reported that Saddam was refusing to co-operate, and a member of the Security Council then exercised its right of veto.

In Davos Mr Powell, apparently responding to concerns from European and Middle Eastern allies, insisted that the US was not rushing to judgement on a war with Iraq.

But he stressed that Washington was determined to disarm Iraq by force, with or without UN backing, if Baghdad did not surrender its arms. "We will not shrink from war if that is the only way to rid Iraq of its weapons of mass destruction."