Bomb threats targeted four European flights Tuesday, leading to the temporary closure of a Warsaw airport, though all planes landed safely and no explosives were found, authorities said.
Two bomb warnings targeted flights bound for Warsaw, the Polish capital, including an SAS Scandinavian Airlines flight from Copenhagen and a LOT flight from London's Heathrow Airport.
In a third incident, Aena, the Spanish airport operator, confirmed an emergency protocol was activated following a bomb alert on a Ryanair flight from Manchester, a northwestern U.K. city, to Murcia, a city in southeastern Spain.
A Wizz Air flight from Bergamo, Italy, was inspected after landing at 9:10 a.m. GMT in Sofia, the Bulgarian capital, a Bulgarian Interior Ministry spokesperson told Agence France-Presse (AFP).
The incidents followed fighter jets scrambling Monday after a Wizz Air flight from London's Luton Airport to Sofia was diverted following a bomb threat and forced to make an emergency stop in Budapest.
The Ryanair flight landed without incident Tuesday in Murcia and Spain's Civil Guard deactivated the emergency plan after checks.
Scandinavian Airlines said it could "confirm a threat against flight SK751 from Copenhagen to Warsaw."
"The aircraft landed normally in Warsaw and the passengers disembarked," it added.
Chopin Airport in Warsaw closed one runway for a security inspection of the plane, but no explosives were found.
The LOT flight, also scheduled for Chopin, diverted to Warsaw-Modlin, the Polish capital's other airport.
Authorities closed the airport following the alert, but the Boeing 737 MAX also landed safely.
"Passengers evacuated and the plane underwent security checks. No explosives were found," Adam Szablowski, a Modlin Airport spokesman, told AFP.
"The airport reopened and is operating normally," they added.
Hungary's Defense Minister Romulusz Ruszin-Szendi said Monday on Facebook that NATO's air defense alert service had issued an alert for the Wizz Air flight from Luton.
"Hungarian Defense Forces' Gripen fighter jets took to the air within minutes, ensuring the passenger aircraft's safe landing in Budapest," he said.
A bomb threat Sunday forced an Austrian Airlines flight from Tel Aviv to Vienna to reroute to Bulgaria. No explosives were found.