By Elizabeth Blunt BBC correspondent at the United Nations in New York

A senior State Department official has said the United States would be prepared to "thwart" the return of UN weapons inspectors to Iraq until the Security Council passes a resolution giving them a new, much tougher mandate.

But does any one Security Council member have the power to prevent the inspectors going back?

If inspectors return to Iraq now, they will be bound by old UN resolutions

Officials working at the heart of the UN system say there are two answers to the question of whether the US can stop the inspectors - one legal and the other political.

Legally, no, they cannot.

The inspectors have their mandate, given to them under past Security Council resolutions, and they continue to carry out that mandate until it is revoked or changed by a new resolution of the council.

A new resolution is, of course, exactly what the US is trying to introduce at the moment, and the difficulty that it is having bears witness to the fact that it cannot do this on its own.

But the political answer is another matter.

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Insiders point out that the inspectorate is the servant of the Security Council, set up by it to do its work.

It makes no sense for Hans Blix and his inspectors to proceed, blindly carrying out their existing mandate, if they can see that the council is unhappy with what they are doing.

So when Dr Blix returns to New York later this week to brief the Security Council, he will also try to get a sense of how the council wants him to proceed, and whether his inspectors should wait a little before they go to Baghdad.

As US Secretary of State Colin Powell said, there is no magic calendar which dictates exactly which day they should do what - and when it comes to political influence, America's superpower status means that the US opinion carries extra weight.