Belgian authorities launched an investigation Wednesday into drone sightings that halted air traffic at several airports overnight, with flights resuming after hundreds of passengers were stranded.
The main airport in Brussels and another in Liege had to suspend arrivals and departures late Tuesday for several hours after suspected drones were spotted nearby.
Dozens of passenger and cargo flights were canceled and some 500 passengers were forced to spend the night at Brussels Airport in the Belgian capital.
Belgium's Interior Minister Bernard Quintin said that investigations were underway to try to identify how many drones were involved in the latest such incident in Europe and who was behind them.
The government was set to hold an emergency meeting of its national security council Thursday to discuss the disruptions.
"The recurrence of drone-related incidents directly affects the security of our country," Quintin wrote on X.
"We must act in a calm, serious and coordinated manner."
The interruptions came after a recent spate of mysterious drone incidents targeting airports and sensitive military locations in several European countries, including Germany and Denmark.
Suspicions have swirled over potential Russian involvement in increased drone activity across Europe, with tension high as the war in Ukraine drags through its fourth year.
Over the weekend, Belgian authorities reported drone activity over the Kleine-Brogel military base, where a number of U.S. nuclear weapons are believed to be stored.
A spokesman for air traffic controller Skeyes told Agence France-Presse (AFP) that flights had been able to restart by the early morning after the interruption.
Some 400-500 passengers had to spend the night at Brussels Airport because of the sightings, airport spokeswoman Ariane Goossens told AFP.
"The situation will return to normal during the day," as flights restart, she said.
A spokesperson for Liege airport – a major freight hub that operates many overnight flights – said the incidents were "worrying for national security."
Flights were able to start again at the airport in the early hours of Wednesday after a six-hour hiatus, spokesman Christian Delcourt said.
Several Belgian media reported that drones were also seen again near the Kleine-Brogel military base Tuesday evening, but that was not confirmed by authorities.
Defence Minister Theo Francken earlier refused to point the finger at Russia for the weekend sightings near the base, but said that they appeared to be a coordinated operation carried out by "professionals."
"They are trying to sow panic in Belgium," Francken told local media. "This is destabilization."
Military intelligence was conducting an investigation into the sightings to try to determine who was responsible.
