The mission, led for the first time by European NATO allies and Canada rather than the United States, could not have been carried out without US support, Anders Fogh Rasmussen said.

“This mission could not have been done without capabilities which only the United States can offer,” the NATO secretary general told a news conference. “For example: drones, intelligence and refueling aircraft.”

“More allies should be willing to obtain them. That is a real challenge.”

Rasmussen said another area in which European allies were particularly deficient compared with the United States was in strategic airlift.

Rasmussen said that despite constraints from defense cuts, such resources were vital for the security of all 28 NATO states and the alliance needed to agree on solutions to fill the gaps at the next NATO summit in Chicago in May.

Rasmussen reiterated a plea for greater cooperation in defense projects to make best use of limited resources, something he terms “Smart Defense.”

The Chicago summit should aim to identify key areas for cooperation and identify nations that would take the lead in specific projects, he said.

“As Libya showed, we can never tell where the next crisis will come from. But we know it will probably come. Any once it does, it maybe too late to start shopping.”

“In Chicago, we must ask NATO heads of state and government for a smart commitment: real and tangible support for more multinational approaches,” Rasmussen said.

While Europe’s two main military powers, Britain and France, have carried out most air strikes in Libya since the United States took a back seat early in the campaign, they have remained heavily reliant on US surveillance capabilities and other support such as air-to-air refueling.

And within weeks of the start of the bombing campaign in March, non-US allies were running short of the so-called “smart bombs” vital to the air effort, prompting a sharp rebuke from the then US Defense Secretary Robert Gates.

In a speech in June, Gates voiced a warning that NATO risked “collective military irrelevance” unless European allies did more to share the burden of defense with the United States.