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 EZY۳۲۴۶ 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.