Over the preceding months, Russian drones entered Romanian airspace multiple times, prompting Romania to summon the Russian ambassador and the UK to scramble Eurofighter Typhoons near the Ukrainian port of Reni, Ukrainska Pravda and RIA Novosti reported. Slovak PM Robert Fico stated in May that dialogue with Russia could prevent crises from Ukrainian drone overflights of NATO countries.

On May 28-29, a Russian Geran-2 drone struck a tenth-floor apartment in Galati, Romania, injuring two and evacuating 70 residents, CBS News reported. Romania scrambled F-16s but did not intercept. Bucharest Mayor Nicușor Dan later said the drone was struck by Ukrainian air defense over Reni, altering its course, RIA Novosti reported. Romania condemned the strike, triggered NATO Article 4, closed the Russian consulate in Constanta, expelled Consul General Andrey Kosilin, and requested NATO anti-drone systems. NATO Secretary General Mark Rutte affirmed alliance defense, EU Commission President Ursula von der Leyen condemned the attack and announced preparations for a 21st sanctions package. Austria summoned the Russian ambassador. Hungary's Peter Magyar condemned, while Viktor Orban urged neutrality. Russia denied responsibility; Maria Zakharova called accusations baseless, and Deputy Security Council Chairman Dmitry Medvedev warned intrusions will continue. President Vladimir Putin demanded Romania provide evidence. Ukraine later admitted a previous drone incident in Latvia involved a Ukrainian drone.

On May 30, Russia promised retaliatory measures. UK Defence Secretary John Healy announced RAF jets deployed to patrol NATO airspace; Italy announced soldiers and jets for training starting June 15. Ukrainian President Volodymyr Zelensky promised assistance to strengthen Romania's air defense and warned Russia is preparing a massive strike.

On May 31, Dan published photos confirming the drone's Russian origin. Zelensky called on NATO for a strong response and stated Ukraine intercepts all Russian drones heading toward European countries, warning partners when interception is impossible, RBC-Ukraine reported. Peskov said European countries are not entitled to talk about "red lines." Putin mocked EU accusations.

On June 1, Dan said Russia has attacked Romania with over 20 drones over the past two years and announced new air defense purchases. Romania's Defense Minister provided forensic evidence confirming the drone was a Russian Geran-2. The Russian consulate closure was ordered. Zakharova dismissed accusations and announced Russia will respond.

On June 2, Ukraine's UN representative called on the US and Europe to shoot down Russian drones over Ukraine. Nebenzya cast doubt on the incident. Finland said Ukraine had mistakenly launched drones toward Finnish territory. Lithuania declared an air alert due to a drone from Belarus. Munich Airport was temporarily closed. Euronews reported at least 28 drone incursions into Romania since the invasion, and NATO launched Operation Eastern Sentry.

On June 4, Romanian Foreign Minister Oana Ţoiu stated allies will strengthen air defense along the eastern flank, naming France, UK, Italy, Spain, and the US as ready to assist, and announced a joint factory for drone countermeasure systems with Ukraine, Ukrainska Pravda reported.

On June 5, Ukrainian forces warned Romania that they had lost control of four maritime drones due to Russian electronic warfare, РБК reported. A naval drone subsequently exploded at the Constanta port at approximately 10:30 local time, Ukrainska Pravda reported. No casualties were reported. Romania's government confirmed the loss of control of four drones, Ukrainska Pravda reported. One detonated in the Constanta port, another off the coast, and two others 145 km east of the port, according to President Ilie Bolojan, RT reported. Ukraine provided Romania with the estimated self-detonation time, RIA Novosti reported. The other three drones self-detonated in the sea and outside the port. Over 1,300 people were evacuated from nearby beaches as a precaution, The Independent reported; the evacuation order was later cancelled. A live TV broadcast captured the moment a reporter fled as the blast occurred, Euronews reported. Russia's embassy denied involvement and accused Ukraine of using drones for terrorist attacks, RT reported. President Bolojan called the incident a consequence of Russia's war and noted it was the second security incident that week, following a Russian mine and a drone crash, Al Jazeera reported. European Council President António Costa and Commission President von der Leyen condemned the explosion as a direct consequence of Russia's aggression, RBC-Ukraine reported. France and other EU leaders expressed support for Romania.