The setback to the anti-war camp came just hours after France and Germany secured a breathing space by forcing the US and Britain to delay tabling a UN resolution - that would authorise war - from tomorrow until at least early next week.

But that gain could be lost by the specialists' verdict on Iraq's Samoud 2 missiles. Although Saddam Hussein has made several concessions to the UN weapons inspectors recently, destruction of the Samoud 2 missiles may prove to be a step too far for him.

Failure by him to comply would almost certainly provide the US and Britain with a casus belli.

A UN security council source disclosed the outcome of a two-day meeting of missile specialists commissioned by the UN weapons inspectors to adjudicate on the Samoud and Fatah missiles. The source said: "The verdict on the missiles was that Al Samoud falls in the prohibited zone and its engines should probably be destroyed."

The UN chief weapons inspector, Hans Blix, who is due to report to the security council again tomorrow, revealed in his last report that Iraq had exceeded its permitted range while testing its missiles. One of the missiles was fired to 183 kilometres. Under the terms of the ceasefire agreement reached after the 1991 Gulf war, Iraq had to destroy all nuclear, chemical and biological weapons and missiles with a range exceeding 150km.

Iraq will argue that the extra 33km exceeded in the test is insignificant and would not enable it to reach targets such as Israel and would thus refuse to destroy the missile engines.

The development came only hours after France and Germany succeeded in securing a brake on the push towards military action. Diplomatic sources said yesterday the US and Britain have been outmanoeuvred in their push for war by delaying a draft resolution, that would deliver a final ultimatum to Iraq to disarm or face military action, until at least Tuesday.

Britain has been at the centre of crafting a resolution that was originally intended to be presented to the security council tomorrow, after Mr Blix delivers his report.

But the hardening stance of the French delegation, with the support of Russia, Germany and China, has forced the UK and US to wait and gauge fellow council members' reaction to the reports before deciding what issues a resolution would need to address to win over the waverers.

"We are looking at what kind of ultimatum would help so long as it doesn't lead to a third resolution," said one diplomat. The likelihood that a draft would be ready by tomorrow is increasingly unlikely, UN security council sources said.

After tomorrow's meeting, diplomats believe there will be contacts between capitals over the weekend and that a draft resolution presenting an ultimatum will emerge on Tuesday or "shortly after". Monday is a public holiday in America.

The US has so far played very little part in helping to draft the resolution. "They don't see a legal need for it," said one security council source. "But politically they recognise it would be useful."

The defence secretary, Geoff Hoon, speaking in Washington after talks with his US counterpart, Donald Rumsfeld, said: "We have made clear we want to see a second resolution. We regard that as being important politically for our own position, but also to build as wide a coalition around the world as we can ... If that second resolution were unreasonably blocked in the security council, we would take the kind of action we took in Kosovo, where we did not have a security council resolution."

The US and Britain can no longer be sure that France will not use its security council veto.

The secretary of state, Colin Powell, said he would press France and Germany to say how much more time they would give the arms inspectors or whether they were only trying to get Iraq "off the hook".