BAGHDAD - New US Defense Secretary Leon Panetta said on Monday that some NATO allies operating in Libya could see their forces "exhausted" within 90 days.

"The problem right now, frankly, in Libya is that ... within the next 90 days a lot of these other countries could be exhausted in terms of their capabilities, and so the United States, you know, is going to be looked at to help fill the gap," Panetta said, speaking to troops in Baghdad.

He did not say which countries he was referring to, or what the US response would be to calls for help.

NATO warplanes have been bombing Libya under a UN mandate to prevent civilians from Muammar Gaddafi's forces, but the alliance is under mounting strain because of the cost of the operation and the failure, after more than three months, to produce a decisive outcome.

Panetta, on his first trip to Iraq since taking the Pentagon's top job on July 1, called on NATO members to do more the ensure the viability of the alliance.

His comments echoed those of his predecessor, Robert Gates, who stepped down at the end of June. Gates warned that NATO risked collective military irrelevance unless allies bore more of the burden for military spending.

"They're going to have to develop their defense capabilities. They're going to have to invest in that kind of partnership as well. We can't be the ones to carry the financial burden in all of these situations. Others have got to do it as well..." Panetta said.

"I'm a believer in partnerships but when you talk about partnerships, you gotta be partners. And that means you got to be able to put up, you know, an equivalent amount of capability so that you can really be partners when we have to go to war."