Romania said on Friday that a drone injured two people in a southeastern city during an overnight Russian attack on neighbouring Ukraine, an incident likely to raise tensions along NATO’s eastern flank.

Romanian President Nicusor Dan called the strike unprecedented and warned that Bucharest would not accept Russia’s war spilling onto Romanian territory. He urged a “firm, coordinated and proportionate” response and thanked EU and NATO allies for their solidarity.

NATO Secretary General Mark Rutte stressed that the alliance stood ready to defend “every inch” of allied territory, calling Russia’s actions reckless and a reminder that the fallout from the war does not stop at Ukraine’s borders.

European leaders broadly echoed that view, with European Commission President Ursula von der Leyen saying Russia’s war had “crossed yet another line” after civilians were injured “on EU territory.” German Chancellor Friedrich Merz called the incident proof of Moscow’s “willingness to escalate” and argued it underscored the need for a stronger NATO presence on the eastern flank.

Romania’s outgoing Prime Minister Ilie Bolojan described the incident as an unacceptable violation of airspace, while EU foreign policy chief Kaja Kallas warned that Russia “cannot be allowed to breach European airspace with impunity.”

Several leaders framed the episode as part of a wider threat to European security. French minister Benjamin Haddad argued Russia was now threatening the continent’s security architecture itself, while Polish President Karol Nawrocki called it another chapter in the “hybrid war” facing NATO’s eastern members.

Italian Prime Minister Giorgia Meloni described the strike as “a very serious act” that endangered European security, and Belgian Foreign Minister Maxime Prevot warned that a weapon hitting an apartment building in an EU and NATO member state marked “a dangerous escalation.”

Ukraine offered support to Bucharest, with President Volodymyr Zelenskiy urging tougher EU sanctions against Moscow. US Ambassador to NATO Matthew Whitaker also reaffirmed Washington’s support for Romania and condemned the “reckless incursion.”

British Foreign Minister Yvette Cooper labelled the incident “extremely dangerous and reckless,” while Estonian Foreign Minister Margus Tsahkna said it highlighted the need to strengthen NATO air defences.

Moldovan President Maia Sandu condemned Russian drones “striking Romanians in their homes,” calling Russia “a danger to all.” Polish Foreign Minister Radoslaw Sikorski remarked that whether deliberate or accidental, the incident showed “Russia is still dangerous and we must defend ourselves against it.”

Slovak Prime Minister Robert Fico struck a more cautious tone, expressing solidarity with Romania while urging restraint and renewed dialogue between the European Union and Russia.