The British government on Monday summoned the Russian ambassador in London following what it described as Moscow’s “unprecedented violation” of NATO airspace.

The Foreign Office called recent incursions into Polish and Romanian airspace “unacceptable” and summoned Russian Ambassador Andrei Kelin.

“Significant and unprecedented violations of Polish and NATO airspace by Russian drones last week, followed by a further incursion into Romanian airspace on Saturday, are utterly unacceptable,” the ministry said in a statement.

“Russia should understand that its continued aggression only strengthens the unity among NATO allies and our determination to support Ukraine. Any further incursions will be met with force,” it added. “Russia must end its illegal war on Ukraine.”

The statement emphasized that the U.K. stands united with Poland, Romania, Ukraine, and NATO allies in condemning these reckless actions.

Multiple Russian drones entered Polish airspace on Wednesday in what European officials described as a deliberate provocation, prompting NATO fighter jets to intercept them. The incident highlighted concerns over the potential expansion of Russia’s more than three-year war in Ukraine.

Although Polish airspace has been violated several times since Russia’s full-scale invasion of Ukraine in 2022, Wednesday’s incursions were unprecedented in scale for Poland or any other NATO country.

Romania reported that it dispatched two F-16 jets on Saturday to intercept a drone that briefly entered its airspace. The country’s defense ministry said the drone did not fly over populated areas and did not pose an immediate threat to the public.