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

The international alliance 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 erratic leader's 42-year rule has 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 members of the North Atlantic military alliance.

"We do not see a lead role for NATO in Libya once this crisis is over," he said. "We see the United Nations playing a lead role in the post-Gadhafi, post-conflict scenario."

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. The resolution did not include any involvement in post-conflict peacekeeping.

French Defense Minister Gerard Longuet said: "NATO has a military vocation and rebuilding Libya is a civilian issue. So really simply, in order to rebuild Libya, if the Libyan people ask for it, because it is first of all an issue for the Libyan people, it is the job for civilian international institutions _ and not military _ to bring a response"

The Libyan rebels, too, have made it clear they have no appetite to see alliance ground forces in the country once the conflict is finished.

But they remain grateful for NATO intervention and applaud the stepped-up alliance bombing campaign, a record 66 strike sorties over Tripoli and environs on Tuesday.

"We've always felt that relentless, continuous strikes would hasten the departure of (Gadhafi) or at least the circle around him," said rebel spokesman Jalal el-Gallal in Benghazi, the de facto rebel capital. "We're very glad that (NATO) is carrying out the actions, and it is a matter of time."

But NATO's campaign has strained the alliance, which was evident Wednesday when U.S. officials said Defense Secretary Robert Gates pointedly prodded five allied nations to share more of the burden of the NATO-led mission in Libya. None committed to do more.

The officials said Gates used his final NATO meeting before retirement to press Germany and Poland to join the military intervention, and Spain, Turkey and the Netherlands to contribute to strike missions against ground targets.

The officials spoke on condition of anonymity to discuss the private meeting of the alliance's defense ministers.

Misrata, a port city and commercial center in western Libya, has seen some of the fiercest fighting in the more than 4-month-old uprising, which has spiraled into a civil war that has divided Libyan into zones controlled by Moammar Gadhafi and others by rebels.

Dr. Khalid Abufalgha of Misrata's central Hikma hospital said government forces attacked the city from three sides _ the east, south and west _ on Wednesday but rebel fighters kept them out. Gadhafi's forces then shelled the city's outlying districts from afar, killing 10 and wounding 24, he said.

All the dead were fighters manning rebel checkpoints outside the city, he said. Most were killed in the village of Tawargha, more than 13 miles (20 kilometers) southeast of Misrata.

The daily death toll is the highest in Libya's third largest city since rebel fighters pushed government forces to the outskirts weeks ago. Misrata remains under siege, able to get food and other supplies only through its seaport.

Misrata is the only large rebel-held city in western Libya. The rebels also control most of eastern Libya as well as a string of towns in the western Nafusa mountain range.

NATO airstrikes thundered down on the Libyan capital on Wednesday, at least four during the day after five before dawn. Another strike hit Tripoli late in the evening.

It was not immediately clear what was targeted. However, NATO strikes appear to be repeatedly pounding the same set of targets: the sprawling Gadhafi compound in central Tripoli, a series of government buildings and radar installations and military bases on the outskirts of the capital.

Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, said NATO remained determined to see the end of Gadhafi's rule. During a visit to Cairo, he reminded reporters of NATO's decision over the weekend to extend the Libyan mission for 90 days, into late September.

"I think it's very clear that NATO is very committed to this mission and committed to providing the kind of protection for the Libyan people that it has when it took the mission on and to focusing on a way to see Gadhafi out the door," he said.

He added that President Barack Obama "has been very clear and remains very clear that this will not involve boots on the ground from the United States perspective."

The pummeling NATO strikes of Tuesday and Wednesday made good on alliance warnings in recent days that attacks would be increasing the scope and intensity. British and French attack helicopters struck for the first time inside Libya over the weekend.

Wing Commander Mike Bracken at NATO's Libya operations headquarters in Naples told The Associated Press there has been "increased tempo over recent days over Tripoli" as the alliance seeks to further weaken Gadhafi's military.

But he stressed that "Gadhafi as an individual has not been a target and won't be a target."

Some 6,850 people, nearly all of them Libyans, have streamed across the border from Libya to Tunisia since Monday to flee the NATO raids as well as fighting between the rebels and government forces, according to the Tunisian Defense Ministry.

In Benghazi, Spanish Foreign Minister Trinidad Jimenez became the latest European official to visit and bolster the opposition forces.

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Corder contributed from Brussels. Associated Press writers Hadeel Al-Shalchi in Benghazi, Libya, and Ben Hubbard and Steven R. Hurst in Cairo contributed reporting.