Its President Volodymyr Zelenskyy said the attack showed why it was “necessary to step up pressure on Russia, so that this war is not dragged out or expanded.” He said Ukraine was “ready to support Romania in whatever way is necessary under these circumstances.”

Meanwhile European Union President Ursula von der Leyen said that Russia’s “war of aggression has crossed yet another line.”

Like most nights, Russia had fired hundreds of drones at Ukraine late Thursday, with the Ukrainian military saying it detected 232 drones and one Iskander-M/S-400 ballistic missile. Of these, Ukraine shot down 217 drones, but 14 of them — as well as the ballistic missile — got through and hit targets in Ukraine, it said.

Meanwhile, Romania radar detected multiple drones crossing into its airspace, the country’s Ministry of National Defense said in a statement. It scrambled two F-16 fighter jets and a helicopter at 1:19 a.m. (6:19 p.m. ET Thursday), with the aircraft having permission to shoot down the drones, it said.

One of the drones hit the roof of an apartment building in Galați, a town on the river Danube that separates Romania, Ukraine and Moldova.

Images backed up official statements that this caused a fire on the roof, with two people injured and needing medical treatment.

What worries officials and experts so much about this type of incident is that — whether deliberate or not — it risks dragging other countries, and potentially NATO, into the war.

Petr Pavel, president of Czechia, said that “mere condemnation” of Russia’s actions was not enough. He instead joined Romania in calling for “a strong international response,” writing on X, “Russia must clearly understand that we will not tolerate such attacks.”

‘Grey warfare’

This is not the first time Russia’s waves of drones, missiles and aircraft have entered other countries’ airspace, with Romania, Latvia, Lithuania, Estonia, Poland and Finland reporting dozens of such incidents since Russia’s full-scale invasion in February 2022.

In 2024, Poland said a Russian cruise missile entered its airspace for 39 seconds, and the next year Estonia said three Russian MiG-31 fighter planes crossed over into its territory for around four minutes.

That one of these drones would sooner or later hit an inhabited area “was inevitable,” former Estonian President Toomas Hendrik Ilves told NBC News in a telephone interview Friday.

He said one explanation was that these drones had “gone off course,” but another was that this was an example of “Russia’s deniable ‘grey warfare.’” Experts say these hybrid tactics include cyber attacks, border incursions and sabotaging everything from undersea cables to civilian railways.

“It’s basically impossible to tell which it is at this point,” he said.

Whatever the intent, Ilves said he thinks “it’s time to take a firmer stand” against Russia. “I’m concerned that we’ve been doing so little in response, and I’m tired of this attitude, ‘Oh no, we can’t do anything because this might escalate,’ when in fact Ukraine has already been invaded.”