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.

“(T)he U.S. government really has demanded the departure of two staff members of the Russian Embassy in Washington, D.C., without presenting any complaints to them. And the U.S. State Department at a high level proposed us not to make this fact public. As you can see, American diplomats don’t stand by their own words,” Ryabkov said, according to Sputnik.

The U.S.-Russia tit-for-tat comes as the State Department on Friday condemned Russian security services for an attack on the American diplomat, the latest incident in what U.S. officials said is increasing intimidation of its personnel.

The U.S. diplomat “was attacked by a Russian policeman” while attempting to enter the American embassy last month in Moscow, Kirby told reporters, speaking just days after a video of the altercation was broadcast on Russian TV.

“The action was unprovoked and endangered the safety of our employee,” he added.

Kirby said that Russian officials’ claims that the policeman was attempting to protect the embassy were “simply untrue.”

He called this a “very graphic and violent example” of two years of “increased harassment” of U.S. diplomats in Russia.

He noted that Washington had initially sought to handle the affair via direct government-to-government channels but said that Russian officials' public allegations compelled the U.S. to make the rebuke public.

He described Russian behavior as “unprovoked and unnecessary.”

“There’s no need for this when there’s so many more important things for us to be working on with Russia,” he added.

Washington had delivered high-level complaints to Moscow about accusations of increasing intimidation of American diplomats in Russia, the State Department said in June.

Secretary of State John Kerry last discussed the matter with Russian President Vladimir Putin on March 24, State Department spokeswoman Elizabeth Trudeau told reporters last month.

“We see an increase and we take it seriously,” she said.

Other Western embassies had reported the same behaviour toward their diplomats stationed in Moscow, Trudeau added.

In June, the Russian Foreign Ministry Spokeswoman Maria Zakharova said Moscow has “felt a significant increase in pressure on the Russian Embassy and consulates general of our country in the United States.”

According to Zakharova, staff members of Russia’s consulate missions abroad “regularly become the objects of provocations by the American secret services, face obstacles in making official contacts and other restrictions,” including travel.

Kirby dismissed the Russian complaints about their U.S.-based diplomats receiving similar treatment, calling the claims “without foundation.”

The Russian embassy in the U.S. did not have any immediate comment Saturday.

The diplomatic incident comes after several recent military close calls between Russia and the United States. In the most recent incident, a Russian ship last week came within 150 yards of a U.S. Navy vessel, the USS San Jacinto, that was sailing in the eastern Mediterranean. The U.S. Navy described the maneuver in a statement as unsafe, “erratic” and “aggressive.”

A few weeks earlier, the Russian Neustrashimyy-class frigate came within 315 yards of the USS Gravely.

And in April, two Russian fighter jets flew within 30 feet of the USS Donald Cook while it was sailing in the Baltic Sea, an action that U.S. Secretary of State John Kerry warned could have led to the jets being shot down.

•Photo shows U.S. President Barack Obama and Russian counterpart Vladmir Putin.

Update news