Russia has expelled Polish diplomats from Moscow for participating in activities that are "incompatible with status", according to the Russian foreign ministry.
The move has been taken by Moscow in retaliation for Warsaw's explusion of Russian diplomats from Poland.
"The Polish authorities indeed took such an unfriendly and absolutely groundless step. The Russian side took appropriate measures and a number of Polish diplomats have already left the territory of our country for activities incompatible with their status," the ministry said.
The ministry offered no confirmation of the number of Polish diplomats that were ordered to leave the country.
Relations between Moscow and the European Union nations continue to deteriorate in light of the Ukraine crisis and the subsequent European Union sanctions after the annexation of Crimea.
Last month, two people were arrested in Poland on suspicion of spying for Moscow. One of those detained is the Russian Defence Ministry's officer, who held access to classified documents regarding Nato and the Polish Army, according to Itar-Tass news agency.