Police launch 'full criminal investigation' into drone sighting at London's Heathrow airport

Police have launched a "full criminal investigation" after a drone was seen at London's Heathrowairport on Tuesday, grounding departing planes for more than an hour.

"Police officers were amongst those who saw the drone," said Commander Stuart Cundyof the Metropolitan Police in a statement on Tuesday evening. "We are carrying out extensive searches around the Heathrow area to identify any people who may be responsible for the operation of the drone.

"I want to be clear that the illegal operation of drones at an airfield is extremely dangerous. Under the Aviation Security Act it is an offence to endanger the safety of an aircraft, anyone found guilty of this offence could face a life sentence," hesaid.

The police first received reports of the drone shortly after 5 p.m. local time (noon ET), Cundysaid, and worked with Heathrowairport to stop airplanes from departing "as a precaution"until investigators determined it was safe.

Although the U.K.'s busiest airport is now "fully operational," the investigation continues as police deploy "significant resources both in terms of officers and equipment to monitor the airspace around Heathrow and to quickly detect and disrupt any illegal drone activity," he said.

The police are getting "military assistance" but will not provide any further details about what that entails.

Cundysaid police were using some of the "learning" gained when drone sightings shut down another London airport Gatwick for three consecutive days before Christmas.

The Gatwick closure led to more than 100,000 people being stranded or delayed, making it the worstdrone-related disruption at an international airport.

British Transport Minister Chris Grayling hassaid the problem at Gatwick had been resolved by "some smart and innovative use of new technology," but he didn't provide details, citing security reasons.

The person or persons responsible for the drones that shut down Gatwick have not been located and no group has claimed responsibility.