TRIPOLI, Libya -- NATO said one of its unmanned drones disappeared over Libya on Tuesday, refuting reports that forces loyal to leader Muammar al-Qaddafi had shot down an alliance attack helicopter.

Libyan state television repeatedly broadcast images of what appeared to be aircraft wreckage, including 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.

"This is the first piece of hardware that I am aware of that has been lost" since NATO's mission began, said Wing Cmdr. Mike Bracken, an alliance spokesman. A U.S. F-15E crashed near the rebel stronghold of Benghazi in March before NATO assumed command of the international intervention in Libya.

Bracken said NATO lost radar contact with an unmanned helicopter drone Tuesday morning along the coast in central Libya, and is investigating the incident.

"This drone helicopter was performing intelligence, surveillance and reconnaissance over Libya to monitor pro-Qaddafi forces threatening the civilian population," Bracken said.

A coalition including France, Britain and the United States began striking Qaddafi'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 Qaddafi'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 Tuesday morning as warplanes roared overhead. It wasn't immediately clear what was hit or whether there were casualties.

What started as a peaceful uprising inside the country against Qaddafi and his more than four-decade rule has devolved into a civil war. Rebels control the eastern third of the country and pockets in the west, and are trying to push their front line forward from their western stronghold of Misrata toward the nearby city of Zlitan.

Qaddafi's forces have countered with barrages of rockets and mortars, and the fighting on the front lines in Dafniya, some 15 miles west of Misrata, has been fierce in recent weeks.

Rockets fired by Libyan government troops have been hitting closer to Misrata this week. On Monday, a rocket struck the front yard of a home in the area of Ruweislat in Misrata, killing a 14-year old boy and burning his mother and brother, according to the boy's uncle, Taher Abu Sheiba.

Pieces of the rocket were laid out on the rubble as children from the neighborhood climbed the broken wall around the home. The smell of smoke hung in the air as family members walked through the destroyed kitchen.

Officials at the front-line hospital in Dafniya said six rebels were killed in overnight clashes, and 50 were wounded.

In London, British Prime Minister David Cameron rebuked military officers who have questioned whether the U.K. can continue its key role in NATO's Libya campaign over the long term.

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 personnel were either deployed or resting following a period of combat duty.