Defence sources in London meanwhile indicated that the coalition's first targets would be the tank convoys closing on Benghazi or ships attempting to bombard the city. Arab participation is likely to be provided initially by Qatar and the United Arab Emirates, although there were already reports as the resolution was passed of Egypt shipping arms to the rebels across the border.

The US is not expected to provide military back-up initially, although it has an aircraft carrier off the coast.

The operation is likely to be mounted from French air force bases in the south of the country - which is less than 1,000 miles from the Libyan coast - as well as from RAF bases in Cyprus. Italy has also said it is prepared to make its military bases available to enforce a no-fly zone.

Arab involvement was a priority for London and Washington, which are anxious to avoid a perception of outside meddling in Arab affairs.