With NATO's campaign in Libya nearing an end, US Defence Secretary Leon Panetta flew to the allied command in Naples on Thursday to confer with officers overseeing the air war.

Panetta called the NATO intervention a "remarkable achievement" and hailed the fall of Moamer Kadhafi's regime after talks Thursday with fellow NATO defence ministers in Brussels.

The Pentagon chief told a news conference that NATO allies were weighing when to halt the bombing campaign and that it would depend in part on the strength of local forces on the ground, who have encircled Kadhafi's loyalists.

He said NATO defence ministers reached a consensus on the conditions for ending the six-month Libya air war, vowing to keep bombing until Kadhafi forces stop attacking civilians and the new leadership can ensure security across the country.

Panetta said there were four "guidelines" for deciding on halting the campaign. The first condition, he said, is "what happens" in the battle for Kadhafi's birthplace, Sirte, one of the last two bastions of the former regime along with the southern desert town of Bani Walid.

The three other conditions included whether Kadhafi forces maintained the capability to attack civilians, whether Kadhafi himself could command fighters and whether the new leadership could secure the country.

Panetta is set to hold talks with Canadian Lieutenant General Charles Bouchard, who is running the Libya air operation, and US Admiral Samuel Locklear, head of allied joint force command in Naples.

NATO Supreme Allied Commander in Europe, US Admiral James Stavridis, based in Mons, Belgium, was also due to join in the discussions in Naples.

Speaking to reporters earlier on his trip, Panetta said he wanted to express appreciation to US and allied officers at the Naples command for their role in what he called a "successful" operation.

After knocking out air defence sites in Libya at the outset of the campaign, the US military assumed a low-profile role in the NATO operation with the British and French taking the lead.

The United States, which carried out about a quarter of all sorties in the six-month campaign, provided crucial support in the form of airborne refuelling of fighter aircraft, surveillance planes -- including unmanned robotic drones -- and specialists to draw up bombing targets.

The United States conducted about 75 percent of all refuelling missions and 70-80 percent of all surveillance and reconnaissance flights, US officials said.

The American military currently has more than 70 aircraft deployed in the operation and more than 7,000 personnel have taken part, officials said.

The Libya campaign offers a stark contrast to the Kosovo war in 1999.

In Libya, European and Canadian aircraft dropped 95 percent of all precision guided munitions while in Kosovo, 95 percent of all munitions were launched by US pilots, a senior NATO diplomat said.