Buckingham Palace says the visit will be rescheduled

Buckingham Palace took the decision on the basis Downing Street advice.

The last time a trip was postponed was in the wake of the 11 September attacks.

On that occasion the Queen was due to attend the Commonwealth heads of government meeting in Australia.

This time the move comes against the background of a possible war with Iraq.

"The visit will be reinstated in due course," said a Palace spokesman.

It's sensible that the head of state should be in this country rather than abroad Downing Street

The trip would have included a visit by the Queen to Nato headquarters in Brussels.

It was scheduled to take place next Tuesday and Wednesday.

A spokesman for Tony Blair said: "The Queen pulled out of the visit to Belgium on Downing Street advice.

"It is an important time for the country and the judgement is that in such circumstances it's sensible that the head of state should be in this country rather than abroad."

He added that the decision was in no way an indication of how the situation with regard to Iraq would develop.