LONDON (Reuters) – Police have arrested a man and a woman after rogue drone operators crippled London’s Gatwick Airport for three days by repeatedly flying onto the airfield, sparking a major security response.

Britain’s second-largest airport was forced to close its runway in the run up to Christmas after drones started appearing on the site south of London in the most disruptive incursion from unmanned aerial vehicles at any major airport.

Police said they had made two arrests late on Friday as part of its ongoing investigation into the criminal use of drones. No group has claimed responsibility for the disruption, which affected at least 120,000 people on Wednesday and Thursday.

The airport, which shut its runway for spells on Wednesday and Friday and for all of Thursday, said it aimed to run a full schedule on Saturday.

However, it warned that passengers should expect delays and cancellations as it continues to recover from the biggest disruption since an Icelandic volcanic ash cloud in 2010.

“We continue to urge the public, passengers and the wider community around Gatwick to be vigilant,” police said.

“Our investigations are still on-going, and our activities at the airport continue to build resilience to detect and mitigate further incursions from drones, by deploying a range of tactics,” they added in a statement.

The pre-Christmas travel disruption began late on Wednesday when Gatwick was forced to cancel all flights after spotting small drones near the airfield. Every time the airport operators sought to reopen the runway on Thursday, the drones returned.

Authorities finally regained control over the airfield after the army deployed unidentified military technology to guard the area, reassuring the airport that it was safe enough to fly.

“Safety is Gatwick’s top priority and we are grateful for passengers’ continued patience as we work to get them to their final destination in time for Christmas,” the airport said.

The drone sightings caused misery for travellers, many sleeping on the airport floor as they searched for alternative routes to holidays and Christmas family gatherings.

The biggest airlines operating at Gatwick include easyJet, British Airways and Norwegian and have said it is too early to determine the financial impact.

Unmanned aerial vehicles have become a growing menace at airports across the world. In Britain, the number of near misses between private drones and aircraft more than tripled between 2015 and 2017, with 92 incidents recorded last year.