Russia is voicing concern about a U.S. warship now just off its shores in the Black Sea.
The guided-missile cruiser USS Monterey, which is taking part in annual joint military exercises conducted by NATO and Ukraine, is an integral part of U.S. plans to create a missile shield in Europe, which Russia opposes.
Russia's Foreign Ministry issued a statement Sunday saying Russia "has repeatedly stressed that we will not leave unnoticed any elements of U.S. strategic infrastructure in the immediate vicinity of our borders and will consider any such steps as a threat to our security."
Russia agreed to consider NATO's proposal last fall to cooperate on the missile shield, but insisted the system be run jointly. NATO rejected that demand and no compromise has been found yet.