Three planes heading for Sofia got bomb threats and were diverted to make emergency landings in Bulgaria, the interior ministry said. So far there is no sign of dangerous items or a real threat on board.
The threats are part of a new series. After the warnings, the authorities followed the security procedure used in such cases.
Two of the planes have landed at Vasil Levski airport in Sofia, where officers are checking them. The third is still in the air and will land at Plovdiv airport. Passengers and crews are expected to go through the usual checks.
The flight-tracking site FlightRadar24 shows a plane from London heading for Plovdiv. Officials have not confirmed that it is one of the planes affected.
Officers are trying to find out where the threats came from. Security is tighter at the airports where the planes are landing, and the investigation continues.
The transport ministry, the airport authorities and police are expected to give more information later today.