Fighter jets were scrambled as dozens of passenger flights were targeted by hoax bomb threats across Europe this week, from Ireland to Bulgaria. Based on statements from airlines, airports, governments, and police forces, Business Insider confirmed 35 airplanes that were threatened. There have likely been more, as some police statements cited unspecified numbers, and some reported incidents could not be immediately confirmed.

The first incident took place on Monday, when a Wizz Air flight from London to Sofia, Bulgaria, was diverted to Budapest, Hungary. An airline spokesperson said a bomb threat was received during the flight, and the plane landed safely before being searched. On Tuesday, another seven flights were threatened. Although Wednesday then appeared quiet, at least 19 airplanes were targeted on Thursday. They included four flights arriving at Prague, the Czech police said.

And in Copenhagen, the Danish police said they searched two airplanes, where "nothing of interest" was found. On Friday, both the police forces said they were also investigating further threats. Madrid Airport received another threat on Friday morning, affecting four flights. Through the week, five flights diverted, but most continued to their intended destinations before being searched. Nobody has been reported hurt, and no bombs or other explosive devices have been reported found.

"We understand that these have been malicious hoax threats," Heidi Alexander, the British transport minister, said on Thursday. The severity of the threats prompted several air forces to scramble fighter jets. On Tuesday, French Prime Minister Sébastien Lecornu ordered fighter jets to intercept an Aer Lingus flight from Dublin which had received a bomb threat, his office said in a statement. The flight, which had 157 people on board and was destined for Rome, diverted to a French air base in Normandy.

Two days later, Bulgaria scrambled jets to intercept three Ryanair flights, one of which was diverted to Plovdiv, the country's second city. The Italian Air Force also sent Eurofighters to escort a Finnair flight from Helsinki to Rome.

"NATO continues to monitor the situation and continues to coordinate closely with Allies, who responded in a variety of ways to the potential threats these last few days, including by scrambling aircraft, some of which were transferred to NATO," said a senior NATO military official.

While a European Commission spokesperson told Business Insider on Tuesday that "it is too early to draw conclusions on whether the reported incidents are linked," some analysts have pointed to hybrid warfare — using covert means to disrupt societies and sow division. Western officials have previously accused Russia of waging a hybrid war against Europe, blaming it for malign operations including attacks, sabotage, arson, drone incursions, and other actions across the continent in recent years.

The Kremlin has repeatedly denied involvement. NATO leadership has said the hybrid war is meant to weaken support for Ukraine and undermine allies' resolve. NATO Secretary General Mark Rutte said last month that the campaign is escalating.

Analysts from Osprey Flight Solutions, an aviation risk management firm, said in a Tuesday note that it is "likely" this week's bomb threats are "a coordinated campaign intended to disrupt aviation operations." "While it is not always clear what drives coordinated campaigns, it is possible that the recent wave is linked to Russian state actors, or to individuals sympathetic to Russia," they added. "Demonstrating a willingness and capability to disrupt aviation is assessed to be consistent with Russia's hybrid campaign in Europe."

Ireland's Cork Airport told Business Insider that it received an anonymous phone threat about a specific flight. And Bulgaria's Border Police told the national news agency BTA that bomb threats were received by email. It remains unclear who is behind the incidents.

The International Air Transport Association, the primary trade group for airlines, released a statement on Thursday, condemning the disruption.

"We urge the authorities to find the origins of these hoax threats," said Nick Careen, IATA's senior vice president for operations safety and security.