Moscow on Saturday said there would be a “harsh” reaction and consequences for Poland’s interests in Russia, after Polish authorities seized a building near Moscow’s embassy in Warsaw — a step Russia labeled “illegal.”

The building, used as a high school for the children of diplomats, belongs to the Warsaw city hall, Polish foreign ministry spokesman Łukasz Jasina told AFP, adding that authorities had acted on a bailiff’s order.

But Russia’s foreign ministry slammed the move as a “hostile” act in violation of the Vienna Convention on Diplomatic Relations and as an encroachment against Russian diplomatic property in Poland.

“Such an insolent step by Warsaw, which goes beyond the framework of civilized inter-state relations, will not remain without a harsh reaction and consequences for the Polish authorities and Polish interests in Russia,” the ministry added.

“Our opinion, which has been confirmed by the courts, is that this property belongs to the Polish state and was taken by Russia illegally,” the Polish foreign ministry’s Jasina told Reuters.