NATO allies are weighing when to call an end to the allied air campaign in Libya with Moamer Kadhafi's forces surrounded and largely out of reach of Western warplanes, officials said Wednesday.

The number of air strikes has dramatically declined in recent weeks, with only one bombing raid reported on Tuesday compared with about 15-20 air strikes a day earlier in the conflict, NATO officials said.

Forces loyal to the deposed dictator are encircled in Sirte and Bani Walid and hiding among the local population, rendering NATO fighter jets less effective and raising the risk of civilian casualties, officials said.

"The effect of air power is not necessarily the right tool with these kind of threats," a Western official, who spoke on condition of anonymity, told AFP.

"You can't hit something that's not there," the official said. "A sniper on a rooftop -- that's not really something we would go after (with air power)."

NATO defence ministers meeting in Brussels on Wednesday are discussing how and when to call time on the six-month campaign, which has been credited with turning the tide in the conflict with Kadhafi, now a fugitive, losing control of the country.

Supreme Allied Commander Admiral James Stavridis was due to offer ministers his assessment of the air war on Wednesday after NATO Secretary General Anders Fogh Rasmussen said he was "encouraged by progress" in the campaign.

"We will continue our operation as long as necessary but we are determined to bring it to an end as soon as possible," Rasmussen said.

Senior military officers overseeing the operation in Naples, Italy, were increasingly eager to call an end to the effort given conditions on the ground, officials said.

But alliance members were still waiting for a clear conclusion to fighting in Sirte and Bani Walid, where National Transitional Council (NTC) fighters are trying to finish off Kadhafi loyalists.

"There's clearly a sense to get it done," said a NATO official, who spoke on condition of anonymity.

A decision to announce an end of the campaign could come later this month if current trends continue, he said.

Wednesday's NATO session was not aimed at deciding a deadline for halting the campaign but was aimed at "taking the temperature" of ministers on how to wrap up the operation, a senior US defense official told reporters.

"There's no agreed check list" that would trigger a halt to the operation, said the official, who asked not to be named.