Italian, French and Bulgarian fighter jets have been scrambled as about 20 commercial flights were hit by a third day of hoax bomb alerts across Europe.
No claim of responsibility was made for all the flights, but threats against flights sent to airports in Rome and Sofia, seen by the Agence France-Presse (AFP) news agency, contained misogynistic messages and claimed to be from "fighters of the Male State".
A British airport also told AFP it received a similar hoax threat, naming the group as Men's State.
The hoaxes particularly targeted low-cost carriers and flights to or from Bulgaria, Czech Republic and Italy.
Three flights were diverted, but all the jets landed safely with no explosives found.
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At least five flights received an air force escort after receiving bomb threats.
Bulgaria's air force escorted three Ryanair planes headed for Sofia from Madrid, Copenhagen, and London. All three planes were inspected and no explosives were found, an interior ministry spokesperson told AFP.
French fighters accompanied an Aer Lingus flight from Dublin that was headed to Rome, forcing it to land at the Evreux military base 100 kilometres west of Paris, the French prime minister's office said.
"Since the pilot did not cooperate as expected with authorities, the Prime Minister immediately ordered fighter jets to intercept the aircraft and escort it," it said.
The Aer Lingus pilot had "allegedly refused" to land at the military base, "preferring a civilian airport", Evreux prosecutor Remi Coutin told AFP.
The airline told AFP Thursday evening that "Aer Lingus and its pilots fully cooperated with the French authorities regarding this matter".
A Ryanair flight from London to Sofia was diverted to Plovdiv Airport, east of the capital, while a Wizz Air flight from Milan to Warsaw was re-routed to Vienna, the airlines said.
A message sent to multiple email addresses for Sofia airport and viewed by AFP said "explosive devices" had been placed on three Ryanair flights headed for Bulgaria.
"You are all accomplices in a criminal conspiracy and for this we want to annihilate you," read the message.
"We, fighters of the Male State, with our actions today will leave a mark in history. Your feminist regime will remember it forever. The explosion will occur in 60 minutes. Today your skies will turn red," it said.
Italian newspaper Il Corriere della Sera published the same text — but with warnings directed at two flights headed for Rome — sent to ADR, the company that manages Rome's airports. A company source confirmed the report to AFP.
A spokesperson for Birmingham Airport in central England told AFP it received a "hoax" threat, that "came from Men's State, similar to others", saying it threatened flights operating at the airport.
There is a far-right movement in Russia called the Male State, but AFP could not immediately confirm any link to the message.
Lou Osborn, founder of Inpact, a non-governmental group which specialises in monitoring clandestine Russian activities, told AFP that the group uses Nazi symbolism and has "thousands of members".
The group in 2021 was designated as an "extremist" organisation by the Russian courts but then supported Russia's invasion of Ukraine the following year.
"Today we don't know to what extent they are connected to those in power," Osborn said.
Prague Airport spokeswoman Denisa Hejtmankova told AFP the airport had received threats in emails from anonymous addresses.
The EU's transport commissioner, Apostolos Tzitzikostas, wrote on X that it was "too early to draw conclusions on whether the reported incidents are linked."
But European authorities say there has been rise in hybrid attacks, sometimes linked to Russia or Iran.
Most of the flights targeted Thursday landed without incident at their original destinations.
Those included a Lot Polish Airlines flight from Warsaw to Brussels, a Wizz Air flight from Milan to Bucharest and an AirSerbia flight from Belgrade to Bucharest.
In the Czech Republic, four targeted planes bound for Prague, flown by Ryanair, Easy Jet and Sky Express, all landed safely.
Danish police said two threatened planes landed in Copenhagen as scheduled.
"Our assessment is that there is no danger, and there has never been any danger, to passengers or anyone else at the airport," Copenhagen police told AFP.
A spokesperson for Heathrow said the airport received a threat that was "deemed not credible".
Travellers at Rome's Fiumicino Airport expressed mixed feelings.
"It's very concerning, we're very concerned about the security in Europe in general, so it's very fearful to be here," Brazilian Natalia Lobo, 29, told AFP.
French traveller Ella Germain, 20, said the news reports had only created "a little bit of worry".
The flights represented a tiny percentage of Europe's air traffic on Thursday. Some 25,072 flights were scheduled across the continent, according to Eurocontrol, the continent's aviation safety body.
On Tuesday, 10 flights were targeted with bomb threats. All turned out to be hoaxes.
The alerts forced the closure of one Warsaw airport and the deployment of Italian air force jets to protect flights.
On Monday, a Wizz Air flight from London's Luton airport to Sofia was diverted due a bomb threat and made an emergency stop in Budapest.
