Nato and its partners, they say, must maintain military operations to protect civilians and maintain pressure on Colonel Gaddafi's government.

To allow him to remain in power, they argue, would be a betrayal of the Libyan people.

Nato has been struggling to find additional warplanes for its mission.

Only a few of its 28 members - including France, the UK, Canada, Belgium, Norway and Denmark - are conducting air strikes.

The alliance's Secretary General, Anders Fogh Rasmussen, told foreign ministers in Berlin he had received no offers from any ally to supply the extra jets but remained hopeful.

Nato pilots are enforcing a UN resolution to protect civilians in Libya, which is split between forces for and against Col Gaddafi since a revolt against his rule began in mid-February.

Fighting on the ground, as well as Nato bombing missions, continued on April 14.