Poland on Saturday said it had seized a high school building near Moscow's embassy in Warsaw meant for the children of diplomats, a move the Russian envoy called "illegal."

The spat over the 1970s multi-storey building, nicknamed the "spy nest" by Warsaw citizens, has been going on for a year.

"This building belongs to the Warsaw City Hall," Polish foreign ministry spokesman Lukasz Jasina told AFP, adding that the move followed a bailiff's order.

The spokesperson for the municipality was unavailable for comment.

Poland says there is a huge disparity in the number of diplomatic buildings each had in the other country.

"This is an illegal act. An intrusion on a diplomatic facility," Moscow's envoy, Sergei Andreyev, told the RIA Novosti news agency.

Andreyev said this was a "violation of Vienna's convention of diplomatic relations."

"Of course, there will be a reaction," Andreyev said, adding that he did not want to give further details and that a decision will be made in Moscow.

"We consider the school by the embassy to be part of our diplomatic mission," he said, saying teachers and staff lived on the territory of the building.

Andreyev said the school will continue to work in a different part of the Russian embassy's premises. "Our priority is ensuring the safety and the interests of our employees and their families."