Libya: Obama, Cameron and Sarkozy vow Gaddafi must go

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.

Col Gaddafi's daughter accused the leaders of "insulting" Libyans.

"To speak of Gaddafi's resignation is a humiliation for all Libyans," Aisha Gaddafi told young loyalists at a rally in Tripoli.

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 Thursday.

'Building pressure'

The BBC's Paul Adams reports from Washington that the letter, published in the UK's Times newspaper as well as the Washington Post and France's Le Figaro, is an unusual step.

Signed by US President Barack Obama, British Prime Minister David Cameron and French President Nicolas Sarkozy, the letter says Libyans in cities like Misrata and Ajdabiya continue to suffer "terrible horrors at Gaddafi's hands".

While the coalition has no mandate to remove Col Gaddafi by force, "it is impossible to imagine a future for Libya with Gaddafi in power", the leaders say; Kazinform cites BBC News.

See www.bbc.co.uk for full version