By Barnaby Mason BBC diplomatic correspondent

As Iraqi President Saddam Hussein reluctantly accepted the United Nations Security Council resolution on weapons inspections and disarmament, differences were already emerging about what might justify military action against Iraq.

Annan: It is up to the UN weapons inspectors to decide

The UN Secretary General, Kofi Annan, told American journalists that any such decision must be seen as reasonable and credible, not as a flimsy or hasty excuse to go to war.

Interpretations of what the Security Council resolution actually means are diverging, just days after the text was finally agreed.

Mr Annan said the US seemed to have a lower threshold than other members of the Council for what would constitute a material breach of Iraq's obligations.

First test

He added that it was up to the UN weapons inspectors to decide what was a serious violation and report it to the Security Council.

British and US planes have patrolled no-fly zones over Iraq since the Gulf War

But the first test will be the declaration Iraq has to make within three weeks of all its chemical, biological, nuclear and missile programmes.

US Secretary of State Colin Powell took a different view from Mr Annan: he told BBC News Online that members of the Security Council, not just the inspectors, could judge whether the declaration bore some relation to the truth.

British officials have also said they would not accept an Iraqi declaration that it had no weapons of mass destruction, as they would not believe it.

Stage set?

But the letter from Iraq accepting the resolution said almost precisely that: it denied US and British allegations that it had produced more such weapons since UN inspectors left four years ago.

So the stage seems set for an early confrontation.

Mr Annan was also sceptical about suggestions from US officials that for Iraq to fire on American and British aircraft patrolling its territory would be a breach of the resolution.

The patrols enforcing no-fly zones have never been authorised by the Security Council.