TRIPOLI, Libya — NATO said one of its unmanned drones disappeared over Libya on Tuesday, disputing reports that forces loyal to leader Moammar Gadhafi had shot down an alliance attack helicopter.Libyan state television repeatedly broadcast images of what appeared to be aircraft wreckage, including shots of a red rotor and close-ups of markings in English.

It quoted an unnamed Libyan military official saying a NATO Apache attack helicopter crashed in Zlitan, about 85 miles east of the capital Tripoli. The report claimed it was the fifth Apache that had been downed — a charge NATO denied.Wing Cmdr. Mike Bracken, an alliance spokesman, said NATO instead lost radar contact with an unmanned helicopter drone Tuesday morning along the coast in central Libya and is investigating the incident. He said the drone was performing an intelligence, surveillance and reconnaissance mission.

"This is the first piece of hardware that I am aware of that has been lost" since NATO's air campaign began, Bracken said. A U.S. F-15E jet crashed near the rebel stronghold of Benghazi in March before NATO assumed command of the international intervention in Libya.A coalition including France, Britain and the United States began striking Gadhafi's forces under a United Nations resolution to protect civilians on March 19. NATO assumed control of the air campaign over Libya on March 31. It's joined by a number of Arab allies.It was not clear whether ground fire or a mechanical failure brought down the drone.

Britain and France began deploying attack helicopters as part of the NATO-led mission earlier this month to boost the alliance's firepower and flexibility against Gadhafi's forces.NATO had previously relied on jets that generally fly above 15,000 feet — nearly three miles high. The attack helicopters give the alliance a key advantage in close-up combat, flying at much lower altitudes. Airstrikes by attack jets remain the backbone of NATO's Libya campaign, however.At least one distant explosion rumbled across Tripoli on Tuesday as warplanes roared overhead. It wasn't immediately clear what was hit or whether there were casualties.

The country's top naval officer last week warned that

British forces might not be able to respond quickly to

new threats if Libyan operations extend beyond

September. On Tuesday, concerns surfaced from

Britain's head of air force combat operations, who said

the air force was running short on pilots and ground

crew staff because so many personnal were either

deployed or resting following a period of combat duty.