Flights across Europe were repeatedly targeted by "hoax" bomb threats this week, disrupting air travel across London, Copenhagen, Dublin, and Helsinki.
Danish police were investigating threats to air traffic at Copenhagen airport on Friday but did not find any immediate danger to passengers, according to reports from Reuters.
"We are once again at Copenhagen Airport today in connection with threats directed at air traffic," police said in a statement, per Reuters. "We are now investigating the incident and have a visible presence at the airport."
Meanwhile, Czech police also said Friday that there were threats to planes departing from and landing in Prague.
At least 27 different flights were impacted on Thursday, according to Reuters, with some forced to land unexpectedly and others escorted by fighter jets.
Aer Lingus, Finnair, Wizz Air and Polish airline LOT confirmed to CNBC that some of their flights were affected.
It comes after seven passenger planes across Europe, two departing from the U.K., were targeted by suspected bomb threats on Tuesday and were described as "malicious hoax threats" by the U.K. government.
Here's what we know so far
Finnair said two of its flights — one from Helsinki to Rome with 144 passengers and 7 crew members and another from Helsinki to Vienna with 177 passengers and six crew members — received "unfounded or hoax" bomb threats on Thursday, with both flights landing safely and customers disembarking the aircraft.
Local authorities in Rome and Vienna inspected the two flights and didn't find anything out of the ordinary.
"Unfortunately, air traffic is sometimes subject to threats, as we have seen this week, when other airlines in Europe have also faced hoax bomb threats," Finnair said in a statement. "Threats are almost always unfounded."
Hungarian budget carrier Wizz Air confirmed to CNBC that its flight from Milan's Malpensa Airport to Bucharest's Otopeni Airport, as well as another flight to Warsaw, were subject to bomb threats on Thursday.
The flight to Bucharest was approaching its final destination and landed safely when the threat was reported at Otopeni, with security checks subsequently clearing the aircraft. Wizz Air's Warsaw flight was diverted.
"This incident comes amid a series of similar bomb threats affecting several airlines across Europe in recent days," Wizz Air told CNBC. "Wizz Air is not the only airline targeted, with other carriers also experiencing threats resulting in flight diversions and security checks."
Irish airline Aer Lingus diverted its Dublin to Rome flight to Normandy on Thursday morning, while Polish airline LOT said two of its flights from Warsaw received security threats. Both were cleared following security inspections, the airlines told CNBC.
Separately, a French prosecutor opened an investigation into whether the pilot of an Aer Lingus plane refused to land in Evreux in northern France following a bomb threat prompting a diversion.
The pilot reportedly refused to comply with the French authorities' directions to land the plane, before being forced by two fighter jets to comply. Prosecutor Remi Coutin said he'll be probing whether the refusal to comply amounts to a criminal offense.
Air France's CEO Ben Smith said none of its flights were affected, but the coordinated threats are unprecedented. "It's unfortunate, and we hope it won't give consumers any reason to slow down or reduce their travel plans."
U.S. Transport Secretary Sean Duffy told CNBC's "Squawk Box" on Thursday that the incidents appeared to be "false attacks."
