Russian President Vladimir Putin's security agencies allegedly have ramped up their intimidation of American diplomats across Europe in ways that would be illegal in the United States: harassment, breaking and entering, and in at least one case, killing a man's dog.

Numerous diplomats said Russian intruders would rearrange furniture or turn on lights and televisions in their homes before leaving, according to a series of memos reviewed by Washington Post columnist Josh Rogin. One diplomat accused an intruder of defecating on his carpet.

Russia stepped up its intimidation campaign in 2014, after the U.S. hit Moscow with sanctions in response to Russia's takeover of Ukraine, State Dept. spokesman John Kirby told the columnist. Most of the incidents unfolded in Moscow, but others reportedly took place in cities outside Russia.

"Harassment and surveillance of our diplomatic personnel in Moscow by security personnel and traffic police have increased significantly," State Dept. spokeswoman Elizabeth Trudeau told reporters Monday. She said other U.S. allies reported similar findings, and that Secretary of State John Kerry has raised the issue with Putin.

An intruder broke into the home of a U.S. defense official in Moscow and killed his dog during President Obama's first term, officials told Rogin.

Diplomats also accused Russian security workers of slashing tires and following the children of former U.S. ambassador Michael McFaul as they went to school.

"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," former U.S. ambassador to the Czech Republic Norm Eisen said. "They are hitting American diplomats literally where they live."

Fox News' Lucas Tomlinson contributed to this report.

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