A Russian Shahed-type drone struck a block of flats in Galati, south-eastern Romania, injuring two people, including a minor, according to the report.
It described the incident as the first confirmed case of a Russian attack causing casualties on NATO-member territory, sharply increasing concern within the alliance.
The strike occurred during large-scale Russian attacks on Ukrainian Danube ports, particularly Izmail, close to Romania's border.
Romania's Defence Ministry said the drone entered Romanian airspace and hit the roof of a residential building in a densely populated area, causing an explosion and panic.
Air defences were placed on alert and two F-16 fighters took off to monitor for further threats.
Bucharest described a serious and irresponsible escalation. Local media called it the most dangerous incident affecting Romanian territory since the Ukraine war began.
NATO and US responses
NATO Secretary-General Mark Rutte spoke with Romanian President Nicusor Dan and said the alliance was ready to defend every inch of allied territory.
He said Russia's actions created risks for the whole alliance and readiness would be strengthened against drones and hybrid attacks.
US Ambassador to NATO Matthew Whitaker condemned the reckless incursion into Romanian territory and reiterated Washington's full commitment to defending allies.
His comments came amid growing concern that an accident or deliberate provocation could trigger an uncontrolled confrontation.
European condemnation
Commission President Ursula von der Leyen called the incident another crossing of limits by Moscow, noting that an inhabited area within the EU had been hit.
She expressed full solidarity with Romania and said Europe could not tolerate attacks endangering civilians on European territory.
French Foreign Minister Jean-Noel Barrot announced that the Russian ambassador in Paris was being summoned.
He accused Moscow of actions aimed at destabilising and intimidating Europe.
Paris linked the incident to mass attacks on Ukrainian cities and growing pressure on European diplomats in Russia.
Italian Defence Minister Guido Crosetto described an unacceptable and dangerous escalation.
He said the security of every NATO and EU member was a shared responsibility.
Rome and other capitals voiced fears that repeated attacks close to alliance borders increased the risk of direct involvement.
Kyiv seeks stronger air defences
Ukrainian Foreign Minister Andrii Sybiha said the incident showed Russian aggression threatened all Europe, especially the Black Sea region, rather than Ukraine alone.
Kyiv called for stronger Ukrainian air defences and tougher sanctions, arguing that protecting Ukraine also shielded neighbouring NATO countries.
A new Black Sea security concern
Russian drones and missile debris have repeatedly been found in Romania during the war.
The report said civilian injuries had not previously been recorded in such incidents on Romanian territory.
Analysts described the event as turning a previously theoretical danger into a concrete NATO security crisis.
There were no indications of an immediate military response against Russia, but increased patrols, surveillance and defensive deployments in Romania and NATO's south-eastern flank were considered likely.
Moscow had not officially commented at the time of publication.
