Story highlights A Russian officials said two Americans were expelled after an "unfriendly move" by the U.S. that was not specified

The diplomatic incident comes after several recent military close calls between Russia and the United States

Washington (CNN) Diplomatic relations between the U.S. and Russia began to unravel after Moscow said Saturday it had expelled two American diplomats and the U.S. revealed it had tossed two Russians in response to an attack on one of its personnel.

"On June 17, we expelled two Russian officials from the United States to respond to this attack," State Department spokesman John Kirby told CNN, referring to an American diplomat who the spokesman said "was attacked by a Russian policeman" while trying to enter the U.S. embassy last month in Moscow.

Russia revealed Saturday it had responded in kind.

According to Russian State News Agency Sputnik, Deputy Foreign Minister Sergei Ryabkov said two Americans were declared persona non grata after an "unfriendly move" by the U.S. that was not specified.

The State Department declined to comment directly on that report.

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