BERLIN - NATO foreign ministers sought to overcome deep differences over the military campaign in Libya on Friday, amid calls for the alliance to show a united front.

United States, British and French leaders, meanwhile, pledged in a joint statement to maintain the military campaign until Moammar Gadhafi leaves.

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The alliance received no immediate commitments Thursday to provide further ground-attack aircraft for the fight despite French and British calls for more intense airstrikes against Moammar Gadhafi's forces.

Friday's main agenda includes meetings with officials from Ukraine and Georgia, and with Russian Foreign Minister Sergey Lavrov.

European Union foreign policy chief Catherine Ashton took part in an opening session early Friday, and the group agreed to schedule an informal EU-NATO meeting to talk further about the Libya situation. No further details were announced.

NATO members agreed Thursday that Gadhafi must leave power but insisted the military mission remain focused on its declared goals of enforcing an arms embargo, protecting civilians and forcing the withdrawal of Gadhafi forces from cities they have entered.

The leaders of the US, Britain and France pledged in the statement published Friday in the International Herald Tribune, The Times, Le Figaro and Al Hayat to maintain the campaign until Gadhafi goes "for good," a display of unity despite European complaints about the low-profile US role.

President Barack Obama, British Prime Minister David Cameron and French President Nicolas Sarkozy said they will not stop the campaign and will "remain united." Writing in the newspaper opinion piece, the three leaders said their mandate under a United Nations Security Council resolution is to protect civilians in Libya.

"It is not to remove Gadhafi by force," they wrote, then added in the carefully worded declaration that: "It is impossible to imagine a future for Libya with Gadhafi in power."

"So long as Gadhafi is in power, NATO must maintain its operations so that civilians remain protected and the pressure on the regime builds," the three leaders wrote.

"Then a genuine transition from dictatorship to an inclusive constitutional process can really begin, led by a new generation of leaders. In order for that transition to succeed, Gadhafi must go and go for good."