TRIPOLI, Libya – Libyan leader Moammar Gadhafi, increasingly cornered under a stunning upturn in NATO airstrikes, lashed back with renewed shelling of the western city of Misrata on Wednesday, killing 10 rebel fighters.

The alliance, meanwhile, said it remained determined to keep pounding Gadhafi forces from the air, but would play no military role in the transition to democratic rule in the oil-rich North African country once the leader’s 42-year rule was ended.

In Brussels, NATO Secretary-General Anders Fogh Rasmussen said Gadhafi’s days in power were clearly numbered, making it imperative for the international community, the United Nations in particular, to gear up to help Libyans establish a new form of government.

“For Gadhafi, it is no longer a question of if he goes but when he goes,” Fogh Rasmussen said at a meeting of the defense ministers from the 28 NATO members.

The alliance said it was acting in the skies over Libya purely in accordance with the U.N. mandate to protect the Libyan people from Gadhafi.

Wednesday’s shelling of Misrata represented an escalation in the more than 4-month-old uprising, which has spiraled into a civil war that has divided Libya into zones controlled by Gadhafi and others by rebels.

Dr. Khalid Abufalgha of Misrata’s central Hikma hospital said government forces tried to enter the city from three sides — the east, south and west — but rebel fighters kept them out. Gadhafi’s forces then shelled the city from afar, killing 10 and injuring 24, he said.