Bomb threats hit at least 20 commercial flights across Europe on Thursday, the second wave to disrupt the continent's air traffic in less than a week, sending fighter jets to escort passenger planes and forcing emergency landings from France to Bulgaria. No explosives were found on any aircraft, and officials and airlines are describing every threat as a hoax — but the scale has alarmed security experts.

An Aer Lingus flight from Dublin to Rome was diverted to the Évreux military air base in Normandy, France, where all 151 passengers and six crew evacuated safely and military bomb disposal teams searched the plane. French Prime Minister Sébastien Lecornu's office confirmed the diversion, according to CBS News. A Finnair flight from Helsinki to Rome carrying 144 passengers was escorted by an Italian fighter jet, prompting Rome's Fiumicino airport to halt flights for 30 minutes, while a second Finnair flight to Vienna landed without incident.

A growing list of airlines and airports

Wizz Air had one flight from Milan to Bucharest land safely after a threat, while a separate Milan-to-Warsaw flight was rerouted to Vienna. Two LOT Polish Airlines flights departing Warsaw were cleared after security inspections found nothing hazardous. Three Ryanair flights bound for Sofia, Bulgaria made emergency landings — two diverted from Madrid and Copenhagen, and a third, originating in London, landed in Plovdiv instead — with Bulgaria's transport ministry confirming nothing was found, per CNBC.

Four more threatened flights, including two EasyJet services from Newcastle and Glasgow, landed safely in Prague. Madrid's Barajas airport reported three affected flights, including two Iberia services, which airport management said were ultimately ruled out as credible. An Air Serbia flight from Belgrade to Bucharest and an Aegean Airlines flight from Athens to Vienna — the latter carrying Greek Deputy Foreign Minister Tasos Chatzivasileiou, who posted that "all is well, everyone is safe" — also landed without incident.

"A VERY DELIBERATE ACT"

Thursday's wave followed at least seven flights targeted earlier in the week, two of them departing the United Kingdom, which Britain's government dismissed at the time as "malicious hoax threats." Air transport security expert Paul Mason told the BBC that threats against passenger planes don't happen that frequently, calling the spate of incidents unusual and indicative of "a very deliberate act" rather than coincidence.

Air France CEO Ben Smith called the coordinated threats "unprecedented" and said he hoped they wouldn't discourage travelers, adding that none of his airline's flights had been affected. U.S. Transportation Secretary Sean Duffy described the incidents as "false attacks" and said American agencies were coordinating with European counterparts. EU Transport Commissioner Apostolos Tzitzikostas said it remains "too early to draw conclusions" on whether the threats are linked, but confirmed the bloc's aviation-security information-sharing mechanism has been activated.

No group has claimed responsibility for either wave of threats, and no government has formally assigned blame. Investigators across multiple countries are now working to trace the source of the calls and emails behind this week's disruptions.