The Russian Foreign Ministry said on January 20 that it would respond to Poland's decision to expel nine Russian diplomats on spying charges, describing it as an "unprecedented step" which hurt bilateral ties.

"The Russian side cannot leave unnoticed such explicitly unfriendly and provocative action," the ministry said in a statement.

"The Polish government should realize that appropriate response measures become inevitable," the statement said.

Nine Russian diplomats were declared "persona non grata" earlier Thursday by the Polish government. They were accused of engaging in "active espionage operations" last year.