By Paul Reynolds BBC News Online world affairs correspondent

Just as US President George W Bush thought he had Saddam cornered, the master tactician has suddenly and unexpectedly agreed to allow United Nations weapons inspectors back into Iraq.

He says that there are no conditions.

And this move has thrown the American strategy into some difficulty.

Saddam's decision makes the threat of US action harder to justify

There is much talk of spanners (or monkey wrenches, if you will) in the works.

Washington has tried to dismiss the Iraqi move as a "tactic which will fail".

And the question has to be asked: does Iraq really intend to give unfettered access or will there be conditions after all?

But in the short term at least the offer will make getting the kind of tough resolution the Bush administration wants from the UN Security Council - with an ultimatum, a deadline and a threat of action - much harder.

And maybe the threat of war this winter will go away.

Inspectors' role

Already Russia has insisted that a new resolution is not necessary. Russia has one of the five vetoes on the Security Council.

The US has been going out of its way over the past few days to stress that getting weapons inspectors into Iraq is not in fact a central part of US policy

And talks between Iraq and the UN on the practical arrangements for new inspections are underway.

The general reaction at the UN and around the world might well be: "Give this a chance."

The return of inspectors from both the UN and the International Atomic Energy Agency is called for in Security Council resolution 1284, passed in 1999.

A special agency was set up to handle the inspections, called Unmovic, or the UN Monitoring, Verification and Inspection Commission.

It is ready to go, but it is likely that Washington will still seek a resolution to try to prevent any wriggle room for Iraq.

End to repression

Such a resolution might lay down a timetable and the absolute requirement that no conditions are set for the inspectors.

Will the return of UN inspectors end the prospect of military action?

Relying on a letter from Iraq assuring the UN that the inspectors will not be hindered is not going to be enough.

Whether a resolution will threaten action in the event of Iraq not complying fully is not at this stage clear.

Some countries might want to wait and see how events develop before issuing threats.

Mr Bush will also stress that Iraq should be carrying out other measures as well, measures he listed in his speech to the UN General Assembly last Thursday.

These include an end to repression, an end to any links to terrorism and either the release of prisoners of war from 1991 or at least accounting for them.

War planning continues

The US has been going out of its way over the past few days to stress that getting weapons inspectors into Iraq is not in fact a central part of US policy.

US Secretary of State Colin Powell said on Sunday that Washington might first want a declaration from Iraq about the state of play on its weapons of mass destruction, something called for by the Security Council resolution 687 of 1991.

So the return of inspectors will not end US pressure.

The question is, will their return stop talk of US-led military action?

Planning for a war will probably continue, because in the long run, the cynics may well be proved right and it might be that Iraq will indeed hinder the work of Unmovic and the IAEA.

In which case the hawks in Washington, who are temporarily back in the nest, will be out flying again.

And regime change will be back on the agenda.