BRUSSELS (Reuters) - NATO, its air power stretched by the heaviest strikes to date on Tripoli, sought broader support for its bombing campaign in Libya on Wednesday but won no immediate new public commitments from allies.
Of the 28 NATO allies only eight, led by Britain and France, have been conducting air strikes against Gaddafi's forces, and a senior U.S. official warned that fatigue was beginning to set in among the aircrews already committed.
A statement from the NATO allies said they would "welcome additional contributions to our common efforts".
A NATO spokeswoman said a number of allies had said they would consider doing more and some had said they would do more, but there were no immediate announcements by nations.
Some allies that have refused to take part in the bombing said they would not alter their stance.
"Germany sticks to its position, no military engagement," German Deputy Defence Minister Christian Schmidt told reporters.
Spanish Defence Minister Carme Chacon said Spain would keep up its role of helping to enforce a Libya no-fly zone and arms embargo, but would not undertake strike missions.
Non-NATO Sweden said it would scale down its role, cutting the number of fighter jets deployed to five from eight and switching their role from patrolling the no-fly zone to reconnaissance sorties.
Norway said last month it would scale down its air strike role after its three-month commitment ends on June 24.
U.S. Defense Secretary Robert Gates, attending his last NATO meeting before retiring, named Spain, Turkey and Netherlands as countries that should consider doing strike missions, officials familiar with the discussions said.
Gates also said Germany and Poland had the capability to contribute to the mission, the officials said.
"He did make the point that certain countries are carrying a large share of the burden ... and you couldn't have the alliance as such expect only eight countries to carry that part of the burden," a senior U.S. official said. "He wanted other countries to look at this issue."
While all NATO allies agree that Gaddafi, who is battling an almost four-month-old rebellion, must go, not all view military intervention as the best way to achieve this.
NATO Secretary General Anders Fogh Rasmussen said he had asked ministers to share the burden and British Defence Minister Liam Fox told reporters "We want to see increased urgency in some quarters in terms of Libya."
Rasmussen said NATO had the military assets needed to continue the operation, but broader backing would make it more sustainable. "The broader the support, the stronger the sustainability," he told a news conference.
NATO says its bombing campaign has greatly reduced the capacity of Gaddafi's forces, but analysts say the conflict could drag on for many months.
Rasmussen said last week he hoped NATO's mission could be completed by the end of September, but many consider that optimistic given the limitations of rebel forces and the fact that NATO has ruled out sending ground forces.
Most of those involved "have vastly underestimated the difficulties and I don't think they anticipated how long this would drag out," said Christopher Schnaubelt of the NATO Defence College in Rome.
"I don't see them increasing the capacity of the rebels to enable them to defeat Gaddafi's forces in centres of power like Tripoli any time soon, so I wouldn't be surprised if NATO was there for years. I think it's 50-50 whether we end up in a frozen conflict and de-facto partition of Libya, with Gaddafi controlling part of it and the rebels the other."
Rasmussen said the international community must begin planning to ensure a peaceful transition after Gaddafi quits.
He said he did not see a lead role for NATO after it had fulfilled its U.N.-mandated mission to protect civilians, and the alliance had no plans to send ground troops as part of a post-Gaddafi stabilisation force.