The intimidation against American diplomats, embassy staff and their families in Russia and other European capitals is increasing, according to the US State Department.

"We see an increase and we take it seriously," State Department spokeswoman Elizabeth Trudeau told reporters at a press briefing on Monday.

"Harassment of US diplomats by host government services is a longstanding problem that occurs inside Russia," according to Trudeau.

She said that Secretary John Kerry last discussed the matter with Russian President Vladimir Putin on March 24.

“Since the return of Putin, Russia has been engaged in an increasingly aggressive gray war across Europe. Now it’s in retaliation for Western sanctions because of Ukraine. The widely reported harassment is another front in the gray war,” said Norm Eisen, US ambassador the Czech Republic from 2011 to 2014. “They are hitting American diplomats literally where they live.”

Former US ambassador to Russia, Michael McFaul, also said that, "It was part of a way to put pressure on government officials who were trying to do their reporting jobs. It definitely escalated when I was there. After the invasion of Ukraine, it got much, much worse.”

Trudeau attributed the increase in such behavior to the imposition of Western sanctions against Russia over the crisis in Ukraine.

Russia's Foreign Ministry, in response, has said that the United States provoked Russian diplomats in the US and elsewhere.

Tensions between Russia and the West peaked after Crimea declared independence from Ukraine on March 17, 2014 and formally applied to become part of Russia following a referendum a day earlier.

The United States and its European allies accuse Moscow of destabilizing Ukraine. Moscow, however, rejects having a hand in the crisis gripping the Eastern European state, Press TV reported.

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