A growing diplomatic spat between the U.S. and Russia has resulted in the expulsion of two American and two Russian diplomats.

The situation began with what U.S. State Department spokesman John Kirby described as an “unprovoked” attack on an American diplomat outside the U.S. embassy in Moscow, which Kirby said, “endangered the safety of our employee.”

Voice of America News describes the attack, which occurred on June 6:

A video released earlier in the week by Russian state television network NTV showed a man leaving a taxi in front of the embassy and being immediately tackled by a Russian guard who came out of a sentry box. The two wrestle on the ground for a few moments before the man is able to crawl through the entrance of the building.

Russia’s Foreign Ministry claimed the guard was attempting to protect the U.S. embassy from a suspicious individual who could have been “a terrorist, an extremist, a suicide bomber,” as spokeswoman Maria Zakharova put it.

The Foreign Ministry now insists the U.S. diplomat was actually a disguised CIA agent, a charge the State Department categorically rejects, along with Moscow’s claim that their policeman thought he was saving the American compound from a suicide bomber.

In late June, the Washington Post wrote of a disturbing “campaign of harassment and intimidation against U.S. diplomats, embassy staff, and their families in Moscow and several other European capitals” by Russian intelligence and security services.

American ambassadors filed complaints about numerous “acts of harassment against their diplomatic staff that ranged from the weird to the downright scary,” including several diplomats who reported, “Russian intruders had broken into their homes late at night, only to rearrange the furniture or turn on all the lights and televisions, and then leave.” In one instance, the Russian interloper defecated on the carpet in a diplomat’s living room.

The Washington Post’s Josh Rogin said a spokesman from the Russian embassy in Washington sent him “a long statement both tacitly admitting to the harassment and defending it as a response to what he called U.S. provocations and mistreatment of Russian diplomats in the United States.”

The situation grew serious enough for Secretary of State John Kerry to bring it up during a March meeting with Russian President Vladimir Putin in Moscow. “Putin made no promises about ending the harassment, which continued after Kerry returned to Washington,” Rogin reported.

This weekend, the State Department revealed that it expelled two Russian officials from the U.S. on June 17 in response to that June 9 scuffle outside the American embassy in Moscow.

The Russians responded by declaring two Americans “persona non grata” after what Deputy Foreign Minister Sergei Ryabkov called an “unfriendly move” by the U.S. According to CNN, Ryabkov didn’t specify what the unfriendly move was.

Russian state outlet RT.com quotes Ryabkov claiming the U.S. government expelled the Russian diplomats “without presenting any complaints to the employees themselves” and “strongly asked us not to make this fact public.”

He also insisted the person who tangled with a Russian policeman outside the U.S. embassy in Moscow was a CIA agent “disguised after conducting an intelligence mission,” who refused to present identification papers when they were demanded and hit the policeman in the face with his elbow. He said this was “a criminal offense” and called the American a “hoodlum.”

Ryabkov added that the other American deported from Moscow was also a CIA operative and was involved in covert actions “targeting Russian diplomats.”