Nato stands ready to defend every inch of its territory, the alliance's chief Mark Rutte said on Friday, after Russian drones hit a residential building in south-eastern Romania overnight.
The incident has drawn condemnations from Nato countries. Romania is a member of the defence pact.
“Russia's reckless behaviour is a danger to us all,” Mr Rutte said in a post on X. “Last night showed yet again that the implications of their illegal war of aggression don't stop at the border.
“We will continue to strengthen our deterrence and defence at home and continue our support for Ukraine as they defend against Russia's aggression,” the Nato Secretary General added.
Escalation
Ukrainian President Volodymyr Zelenskyy said he stood ready to support Romania “in whatever way is necessary”. The neighbouring countries share a 610km land border.
German Chancellor Friedrich Merz condemned Russia's “reckless” drone attack, saying it showed Moscow's willingness to escalate.
Nato leaders were cautious about whether the incident was worth triggering the alliance's collective defence clause.
French Foreign Minister Jean-Noel Barrot suggested it could have been an accident.
“This is an irresponsible act with a drone and it's not the first – in the past months several times Russian drones have gone astray in European and Nato skies,” he told radio station France Inter.
Mr Barrot said he had summoned the Russian ambassador for an explanation.
UK Prime Minister Keir Starmer called it a “serious violation of Nato airspace”.
“Russia’s aggression against Ukraine and attacks on civilians and civilian infrastructure threatens the security of our entire continent," he said.
“Time and again, Russia has shown it has no regard for civilian life, for international law, or for the sovereignty of its neighbours. That must not be allowed to stand.”
Some Ukrainian drones have strayed into Baltic countries' airspace in recent weeks, causing confusion and raising tension with Russia.
The incident injured two people in an attack launched by Moscow on neighbouring Ukraine.
It is the first time in the war that a drone has hit a densely populated area in Romania, also a member of the European Union, and caused injuries. The incident has increased tension on Nato's eastern flank at a time when Ukraine's allies are worried about the conflict spreading further.
The drone hit the roof of a 10-storey apartment block in Galati, near the border with Ukraine, and caused an explosion, Romanian authorities said.
“Initial information indicates that the entire load of the Geran 2 drone, of Russian origin, exploded upon impact,” the country's Defence Ministry said.
Romania has recorded 28 cases of Russian drones breaching its airspace since Moscow began attacking Kyiv's ports across the Danube, the ministry added.
Romanian Foreign Minister Oana Toiu called the incident a “serious violation of international law” and said Bucharest “requested measures to accelerate the transfer of anti-drone capabilities to Romania”. She said the Russian ambassador had been summoned to her ministry.
Prime Minister Ilie Bolojan said his country would strengthen its anti-drone programme using an EU financial instrument.
There was no immediate comment from the Russian Defence Ministry.
F-16 jets scrambled
The Romanian Defence Ministry said it scrambled two F-16 fighter jets and a military helicopter to monitor the attack, with the pilots authorised to shoot down any drones. Residents of the Braila, Galati and Tulcea border areas were warned to seek shelter.
Romanian Brig Gen Gheorghe Maxim said at a news conference that the drone was in the country's airspace for four minutes, flying low, making it difficult for radar to detect. He said the US anti-drone system, Merops, was operational, but would have been too risky to use in a city.
The impact of the drone caused a fire on the roof of the building, Romania's emergency response agency said. Two people were treated on site and 70 were moved to safety, the agency added.
State news agency Agerpres quoted Galati's emergency response agency as saying a woman and her child had been taken to hospital with minor injuries. Two people were treated on site after experiencing panic attacks.
Galati was last hit in April, when a drone damaged an electricity pole and a household annex, leading to the evacuation of residents. Officials retrieved the drone to detonate its payload remotely.
Drone damage
Romanian Deputy Interior Minister Raed Arafat, who is in charge of the emergency response agency, told broadcaster Digi24 that the incident also damaged five cars.
In a separate incident, a drone without an explosive charge was found near Basesti in north-western Romania, state TVR broadcaster reported late on Thursday, quoting local authorities. The area was secured.
Officials are investigating the origin of the drone, which the report said had a wingspan of about three metres, TVR added.
Ukrainian authorities, meanwhile, said the port at Izmail in the Odesa region came under attack from several drones early on Friday. Izmail, close to the Romanian border, is home to Ukraine's largest Danube port and faces frequent attacks.
