German police have arrested three passengers for allegedly discussing “terrorist matters,” on an easyJet flight from Slovenia to the UK. The flight from Ljubljana to London Stansted airport was forced to land in Cologne over security concerns.

“EasyJet can confirm that flight EZY3246 from Ljubljana to London Stansted diverted to Cologne today,” the airline said in a statement according to ITV news.

The incident happened mid-flight, when passengers allegedly overheard the three men having a “suspicious conversation” discussing terrorism-related issues, using the words “bomb” and “explosive.” They immediately alerted the crew.

The captain then made the decision to divert the Airbus 319 to Germany as a “precautionary” measure, so that the aircraft and passengers could undergo additional security checks.

On arrival at Cologne-Bonn airport at about 6:30pm on Saturday, all 151 passengers on board were evacuated via the emergency slides where they were met by police.

“The three suspects were arrested,” Cologne police said in a statement. A backpack belonging to one of the men was seized and later destroyed in a controlled explosion police said, according to Reuters.

The incident forced Cologne airport to suspend operations for three hours. Ten flights were diverted to other air hubs in the area as a result.

A passenger traveling on board easyJet flight told Sky News that at around 3am local time Sunday, the passengers were still grounded.

“We plan to operate the flight tomorrow morning and so are providing all passengers with hotel accommodation and refreshments along with regular updates,” easyJet said.