Multiple planes across Europe were diverted and forced to make emergency landings Thursday because of bomb threats that have turned out to be unfounded.

At least 11 planes, originating from cities including Copenhagen, Dublin, Helsinki, Madrid, Milan and Warsaw, have been affected. The source of the threats was not immediately clear.

These incidents came after several flights in Europe received similar warnings on Tuesday that the U.K. government described as "malicious hoax threats."

"Upon receiving a threat regarding the placement of an improvised explosive device on board 4 aircraft heading to Prague, we are preparing with colleagues from Prague Airport for their landing. We assess the relevance of the threats as low," Czech Police wrote on X, before adding that inspections of the planes yielded "negative results."

The threats come at a time when European officials have been blaming Russia and Iran for "hybrid attacks" and acts of sabotage, which both Moscow and Tehran deny, Reuters reported.

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Earlier, a flight from Dublin to Rome was diverted to a military air base in western France because of a bomb threat, according to French Prime Minister Sebastien Lecornu’s office. That flight landed safely at the base in Evreux in Normandy, with all 151 passengers and six crew members disembarking, the office said.

A LOT Polish Airlines flight from Warsaw to Brussels landed at its destination, where inspections found no hazardous or suspicious items, the airline said.

A Wizz Air flight from Milan to Bucharest landed safely in Bucharest following a bomb threat, according to airport spokesperson Teo Postelnicu.

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Finnair said that Flight 1761 from Helsinki to Rome was targeted by a bomb threat, but nothing was found after it landed in the Italian capital.

Three Ryanair flights bound for Sofia, Bulgaria, had to make emergency landings because of bomb threats on board.

Two of the flights — one from Copenhagen, Denmark, and the other from Madrid — landed safely at Sofia’s Vasil Levski Airport, airport officials told reporters. The third Sofia-bound flight, from London’s Stansted Airport to Sofia, had been diverted and landed safely at the airport in Plovdiv, Bulgaria’s second-largest city, Plovdiv Airport CEO Krassimir Peshev said.

The Associated Press contributed to this report.