Russia on Sunday protested the arrival of a US Navy cruiser equipped with a ballistic missile defence system in the Black Sea to take part in naval exercises with neighbouring Ukraine, saying it was a threat to its national security.
"We have a number of questions regarding the arrival in the Black Sea of the US Navy cruiser Monterey equipped with the Aegis anti-missile system to participate in the Ukrainian-US Sea Breeze 2011 exercises," the Russian foreign ministry said.
"The Russian side has repeatedly stressed that we will not let pass unnoticed the appearance of elements of US strategic infrastructure in the immediate proximity to our borders and will see such steps as a threat to our security," it said in a statement.
The protest comes as Russia and the West failed this week to reach a breakthrough on a missile shield project for Europe with Moscow complaining that its demands were falling on deaf ears.
In 2009, US President Barack Obama said he would shelve his predecessor's plans to site parts of a missile defence shield in Poland and the Czech Republic, and instead deploy more mobile equipment targeting Iran's short and medium-range missiles.
The foreign ministry noted it understood that the stationing of the Monterey in European waters was part of the US missile defence shield plan but added it did not see why the warship had to be so close to its borders.
"According to an official US version, they [warships] can be deployed to the Black Sea in case of necessity, for example, in case of a flare-up in the region," the statement said.
"We would like to understand what 'flare-up' the US commanders had in mind when they moved the primary striking unit of NATO's future anti-missile system from the Mediterranean to the east?" it said, noting the aim of the naval exercises was to practice anti-piracy raids.
Russia has expressed fears that the planned anti-missile system would be directed against its defences, with the dispute threatening a rapprochement between Moscow and the Western alliance.
Moscow has recently said it would be ready to drop its opposition to NATO installing missile defence facilities in Europe if it provided legal guarantees the system would not be directed against Russia.
NATO has rejected the proposal, saying legal guarantees would be hard to put on paper.
The Russian foreign ministry said Monterey's arrival in the Black Sea demonstrated blatant disregard for Moscow's concerns.
"It is being done deliberately, as if to show to Russia that no-one is going to take its opinion into account," it said.
"The reconnaissance by US anti-missile ships of the Black Sea waters confirms once again the need to work out precise legal guarantees of the anti-missile system deployed in Europe not being directed against Russia's nuclear containment shield"