WASHINGTON -- A U.S. official has told RFE/RL that a U.S. diplomat was tackled and injured by a Russian security service guard outside the U.S. Embassy in Moscow earlier this month in what appeared to be an unprovoked attack.

The June 6 incident came amid an increasing number of tense encounters between U.S. diplomats and Russian security officials in Moscow and elsewhere, something that U.S. officials have complained openly about in recent days.

In the incident, which was first reported by The Washington Post, the diplomat had just shown his embassy badge to the guard, one of several that help monitor the perimeter of the massive U.S. Embassy complex and who work for the Federal Security Service (FSB), the country's main security agency.

The guard then tackled the diplomat, leaving him with a broken shoulder. The diplomat was able to walk into the embassy compound under his own power and he later left the country for medical treatment, according to the official, who was not authorized to speak publicly.

"It was definitely intentional," the official told RFE/RL.

Diplomats in Moscow and Washington have met with their Russian counterparts to complain about the incident and others that come as U.S.-Russian relations sink to their lowest point since the Cold War, following sanctions imposed against Russia for its actions in Ukraine and increased NATO and Russian military presences on each side of Russia's western border.

U.S. diplomats in Moscow have reported being pulled over by Moscow traffic police about five dozen times over the past month, an unusual number in a city where diplomats are usually afforded leeway for things like minor traffic violations.

The embassy spokesman this week reported returning home to find cigarettes in his apartment; another official reportedly returned home to find the water taps turned on.

Comments by Russian Foreign Ministry spokeswoman Maria Zakharova suggested deeper ongoing problems when she blamed the United States for the current tensions.

"Diplomacy is based on reciprocity. The more the U.S. damages relations, the harder it will be for U.S. diplomats to work in Russia," she told a briefing in Moscow on June 28.