After briefing British Prime Minister Tony Blair in Downing Street, the chief inspector Hans Blix and the head of the International Atomic Energy Agency Mohamed El-Baradei said they needed "100% co-operation" from the Iraqis if there was to be a peaceful resolution to the current crisis.
Dr Blix and Dr El-Baradei stopped off in London on their way to Baghdad for crucial talks with Iraqi officials this weekend which could represent the final chance to head off war.
The inspectors are due to deliver a report to the UN Security Council the following Friday February 14 which could seal Iraq's fate.
"We hope that at this late hour they will come to a positive response. If they do not do that, then our reports next Friday will not be what we would like them to be," Dr Blix said after the meeting with Mr Blair.
Dr El-Baradei added: "I think the message coming from the Security Council is very clear: that Iraq is not co-operating fully, that they need to show drastic change in terms of co-operation.
"The message also coming from the Security Council is that time is very critical, and that we need to show progress in our report due on the 14th of this month.
"So our mission, I think, in Baghdad this weekend is crucial and we hope we will secure full 100% co-operation on the part of Iraq."
British Foreign Secretary Jack Straw brushed aside French calls to triple the number of inspectors in a final attempt to disarm Iraq without the use of military force.
"The issue before Iraq now, and the issue before the Security Council, is not one of more time for the inspectors or more inspectors; it is about much, much more co-operation from the Iraqi regime," he said.
He said that if Iraq did not comply with Security Council resolution 1441 on disarmament, then the Security Council would have to "face up to its responsibilities".
"If we are to ensure that the world is governed by law and not by the rule of the jungle, then sometimes, and this may be one occasion, international diplomacy has to be backed by the threat, and if necessary the use, of force," he said.
In Washington, US Secretary of State Colin Powell yesterday told senators that "within weeks" the Iraq stand-off situation will be brought to a conclusion "one way or another".
US and British military preparations received a welcome boost with a vote by the Turkish parliament to allow the US to start renovating military bases in the country a first step towards allowing US combat troops. It followed the announcement by NATO that military planning could start next week by the alliance to protect Turkey in the event of a war with Iraq.
France, Germany and Belgium had been holding up the move for the past three weeks, arguing it would send the wrong signal while the UN was trying to find a peaceful solution. NATO Secretary General George Robertson said they had agreed a "silence procedure", with planning starting automatically unless any of the alliance members raises an objection. "I'm confident we'll reach a decision early next week," he said.