The leaders of the United States, Britain and France have said in a joint letter that there can be no peace in Libya while Muammar Gaddafi stays in power.
Barack Obama, David Cameron and Nicolas Sarkozy say NATO must maintain military operations to protect civilians and maintain pressure on Colonnel Gaddafi.
To allow him to remain in power would "betray" the Libyan people, they write.
NATO pilots are enforcing a United Nations resolution to establish a no-fly zone and to protect civilians in Libya. The country has been split between forces for and against Colonel Gaddafi since a revolt against his rule began in mid-February.
The BBC reports signs of division remain within NATO, which is struggling to find additional combat aircraft for its strikes.
On Thursday Colonel Gaddafi's daughter appeared before cheering crowds and accused the Western leaders of "insulting" Libyans.
The letter comes at a time of growing unease at the failure of Western military action to dislodge Colonel Gaddafi and tensions within NATO over the reluctance of certain members to do more.
The letter from the three leaders was published in the The Times newspaper in Britain as well as the International Herald Tribune and France's Le Figaro.
Only a few of NATO's 28 members - including France, Britain, 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 said he remained hopeful.
The letter says Libyans in cities including Misrata and Ajdabiya continue to suffer "terrible horrors at Gaddafi's hands".
While the coalition has no mandate to remove Colonel Gaddafi by force, "it is impossible to imagine a future for Libya with Gaddafi in power", the leaders say.