Police have opened an investigation after Heathrow airport was forced to ground departures because of a drone sighting – less than three weeks after a series of similar reports at Gatwick affected about 1,000 flights.

The armed forces were called in to protect the UK’s busiest airport as Scotland Yard said on Tuesday evening its officers were among those who had seen the device in the air.

The Metropolitan police commander Stuart Cundy said: “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.

“We are deploying 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; some of which are as a result of learning from the incidents at Gatwick.”

Cundy would not elaborate on what forces had been deployed and the Ministry of Defence said only that “specialist equipment” had been sent to Heathrow, west London, at the request of the police.

It is believed that the armed forces used the Israeli-developed Drone Dome system, which can detect and jam communications between a drone and its operator, at Gatwick in December.

A spokeswoman for Heathrow said the runway had been closed as a precautionary measure shortly after 5pm, as staff worked with the Met to investigate the report. At about 6pm, the runway had reopened. Inbound flights were not affected.

While the disruption at airport on Tuesday evening was less severe than that caused in the run-up to Christmas, when 140,000 people were affected by repeated closures at Gatwick, the latest incident raises further questions about the UK authorities’ preparedness to protect vital infrastructure from the devices.

Besides the military deployment, the junior transport minister Liz Sugg was due to meet the heads of the UK’s main airports on Thursday to discuss their plans to deal with drones. Preparations for the meeting began last week in the aftermath of the Gatwick disruption.

On Monday, the government announced that police were to be handed extra powers to combat drones near airports, giving them power to land, seize and search the devices. The Home Office was due to begin testing and evaluating the use of counter-drone technology at airports and prisons.

Last week, Heathrow and Gatwick said they had invested significant sums of money in military-grade anti-drone technology. While it would not offer details on exactly what equipment had been installed, Gatwick said it had purchased a system that offered a similar level of protection to that offered by the armed forces during the pre-Christmas disruption, while Heathrow was understood to have invested in similar equipment.

Also last week, the transport secretary, Chris Grayling, chaired a meeting of defence chiefs, the police and Home Office officials to discuss the issue.