What to know about the hoax bomb threats that targeted flights in Europe

Bomb threats targeted dozens of flights across Europe this week following a string of hoaxes that caused flight diversions and forced airlines to scramble to keep passengers safe and air traffic disruptions minimal.

Fake bomb threats are relatively common , but it is unusual to see so many in such a short period. No suspicious items were found and no one has been injured, but the threats raised concerns because they came on the heels of other European disruptions — including attacks on supermarket refrigeration systems and drone incursions .

With unanswered questions hanging over the continent — it was not known whether the threats were linked, who sent them or what they hoped to achieve — security experts were to meet in Brussels next week to discuss measures to deal with the hoaxes.

Here's what to know:

The hoaxes have led to plane searches and diversions, and, in some cases, emergency landings and military escorts.

Still, the European air traffic authority insisted that overall, the threats caused minimal disruption to aviation.

Separately, three broadcasters — the Irish national broadcaster RTE, the U.K.-based Sky and NOVA TV, a private broadcaster in Bulgaria — also received security threats on Friday, a possible sign the menace was spreading beyond the skies.

It remains unclear who is behind the airline threats, which come at a time of increased geopolitical tensions and warnings from authorities that Russia may be ramping up its so-called hybrid threats in Europe — a mix of covert and indirect attacks attributed to Moscow and meant to destabilize European countries.

Authorities haven’t attributed the threats to any group or state actor, and no evidence has emerged linking the hoaxes to a government. An email containing the threat sent Thursday to airport authorities in Rome and reviewed by The Associated Press purported to come from a group describing itself as anti-feminist and claiming it was targeting a “feminist regime.”

Another European airport received a threat with similar wording, but it was unclear if it came from the same sender.

In Amsterdam, meanwhile, the Dutch Marechaussee military police detained a man on Thursday night at Amsterdam’s Schiphol Airport in connection with a threat to a flight that was about to leave for Prague, Marechaussee spokesperson Doron Wallin said Saturday.

It was not clear if the threat was linked to other recent hoaxes. Wallin said the Marechaussee regularly deals with fake bomb threats. The aircraft flew on to Prague later in the evening and the man was released the following day.

Matthew Borie of Osprey Flight Solutions, which advises airlines on flight threats, said he had several hypotheses for the incidents — ranging from a single threat triggering copycat incidents to an individual or a group making multiple threats, and “hybrid warfare” operations by state actors or their supporters.

The focus on Europe means “there could be a Russian angle,” said Borie, the company’s co-founder and chief intelligence officer. “We need to keep in mind, though, that Iranian hybrid warfare is just as active in certain pockets of Europe as well.”

His message for travelers?

“Don’t be alarmed,” he said, noting that national authorities have “coordinated response mechanisms,” including, at times, the deployment of NATO fighter jets to escort such planes.

Jacob Funk Kirkegaard, a senior fellow at the Bruegel think tank in Brussels, said the threats were “stress-testing” how European governments and airport officials respond, and whether their responses were coordinated.

The idea behind the threats “appears to be to sow chaos, uncertainty, about the reliability of air traffic across Europe” and could have “cascading effects” — such as economic damage and costs related to inspection, investigation and the cleaning of aircraft.