A Russian Foreign Ministry official says Moscow views Romania as a NATO outpost and a "clear threat" because it hosts part of a U.S. missile shield in Europe.
"Romania's stance and the stance of its leadership, which has turned the country into an outpost, is a clear threat for us," Aleksandr Botsan-Kharchenko told the Interfax news agency in remarks published on February 9.
In May 2016, the U.S. military activated a missile-interceptor site in Romania -- a key element of the missile shield, which is due to be fully operational in 2018.
The United States says the shield will protect NATO members against short- and medium-range missiles, particularly from rogue states in the Middle East, and poses no threat to Russia.
Russia dismisses this and claims the true aim is to weaken its nuclear deterrent, upsetting the balance of power.
"All these decisions...are in the first instance aimed against Russia," said Botsan-Kharchenko, the head of the Russian Foreign Ministry department responsible for ties with Romania and several of its neighbors.
Botsan-Kharchenko also accused Romanian authorities of reveling in anti-Russian rhetoric, and said Russia had made clear to Bucharest that it was unhappy with Romania's stance.
Moscow's comments come as NATO deploys thousands of soldiers and heavy weaponry to Poland, the Baltic states, and southeastern Europe in its biggest buildup since the Cold War.
U.S. and NATO officials say the move is needed to provide extra security and reassurance to European countries after Russia's 2014 annexation of Ukraine's Crimea, but Russia says it is part of an aggressive strategy on its borders.
Based on reporting by Reuters and Interfax