The Nato secretary general, Mark Rutte, has said the alliance is “ready to defend every inch” of its territory after a Russian drone hit an apartment building in Romania, a member state, during an overnight attack on neighbouring Ukraine.

“Russia’s reckless behaviour is a danger to us all,” Rutte wrote on social media after a call with the Romanian president, Nicuşor Dan. “I affirmed that Nato stands ready to defend every inch of allied territory.”

On Friday, Dan convened an emergency meeting of the country’s supreme council of national defence, and the foreign ministry summoned Russia’s ambassador.

The incident in Galați, which injured two people, prompted swift condemnation and the threat of repercussions, even as Vladimir Putin attempted to suggest, without evidence, that the drone might have been a stray Ukrainian weapon.

Romania’s foreign minister, Oana Țoiu, said on X: “We will officially communicate the consequences that this lack of responsibility on the part of the Russian Federation will have for the diplomatic relations between our countries, as well as the next steps at the European level regarding sanctions packages.”

The foreign ministry said it had asked Nato to accelerate the transfer of anti-drone capabilities and suggested it would call on article 4 of the Nato treaty, which would trigger formal discussions within the organisation about threats to Romania’s security.

It described the incident as a “grave and irresponsible escalation” and a serious breach of international law.

The strike in Romania is the latest example of the war in Ukraine spilling beyond the country’s borders, amid growing concern over Russia’s wider campaign of hybrid warfare across Europe.

Gen Gheorghe Maxim, a stand-in commander for the Romanian armed forces’ joint staff, told a news conference on Friday that the strike in Galati was not “an attack from Russia against Romania”, but that “Romanians should understand that Russia is a threat to the security of the countries in the area.”

Speaking later on Friday, Putin told reporters he had only just heard of the incident, and suggested the drone wreckage should be handed over to Russia so it could conduct its own independent investigation.

The incident came as Russia threatened to intensify its systematic strikes against Ukraine.

Romania’s defence ministry said the drone was tracked by radar in Romanian airspace before it crashed into the roof of a residential building in Galați on Friday. The impact sparked a fire, injured two people and forced the evacuation of several residents from the building.

Police and emergency services responded at the scene. Galați is on the Danube River, west of the borders with Moldova and Ukraine.

Dan said his country would not accept the war of aggression waged by Russia against Ukraine being transferred to its citizens. He said he had instructed the foreign ministry to prepare a package of measures regarding Romania’s relationship with Moscow, “proportionate to this very serious situation”.

France’s foreign minister also denounced the incident. “I want to condemn this irresponsible act by Russia,” Jean-Noël Barrot told the broadcaster France Inter, adding that the drone had struck “a country of the European Union and a Nato country”.

The European Commission president, Ursula von der Leyen, said Russia’s “war of aggression has crossed yet another line”. “We stand in full solidarity with Romania and its people,” she wrote on social media. “As we continue strengthening our security and deterrence, especially on our eastern border, we will keep increasing the pressure on Russia.”

Ukraine’s foreign minister said the incident showed Russia posed a threat to the whole of Europe. “The recent incursion of a Russian drone into the Romanian airspace and its explosion … proved once again that Russian aggression poses a real threat to the Black Sea region and the entire Europe,” Andrii Sybiha said in a post on X.

The Romanian military scrambled two F-16 fighter jets and a helicopter authorised to engage targets, while emergency alerts were issued to residents in the affected areas. The government reiterated that it had asked Nato to speed up the delivery of anti-drone systems to Romania.

On Thursday the UN secretary general told the security council that in the first four months of this year more civilians had been killed in Ukraine than in the same period in 2025, 2024 or 2023.

António Guterres called for greater diplomacy, immediate de-escalation and “a full and unconditional ceasefire”, warning of “unknown and unintended consequences” from the escalation and intensification of attacks.

Russia has been using long-range ballistic missiles and drones to damage Ukraine’s power grid and hammer cities, and Ukraine has been bracing for further heavy bombardments.

The Ukrainian president, Volodymyr Zelenskyy, said on Thursday that he was pressing the US to provide additional Patriot air defence missiles to counter Russian ballistic missile attacks.

Associated Press and Reuters contributed to this report