Poland on Saturday confiscated the building of a Russian secondary school in Warsaw, the Polish Foreign Ministry said.

"This building will henceforth belong to the Warsaw municipality," ministry spokesman Lukasz Jasina told AFP by telephone.

Russia denounced the "illegal act" by the Polish authorities, after confiscating the building of a Russian school in Warsaw, and vowed to respond to it.

"This is an illegal act, the storming of a diplomatic site," said the Russian ambassador to Warsaw, Sergei Andreev, in a video clip published by the Russian state news agency, RIA Novosti. He warned that Russia would respond based on the "principle of reciprocity."