Washington, Feb 16 (IANS): A Russian spy ship sits 30 miles off the US coast of Connecticut, according to an American defence official.

This is the farthest north the Russian spy vessel has ever ventured, the official told CNN on Wednesday.

The Leonov, which conducted similar patrols in 2014 and 2015, was off the coast of Delaware, but typically it only travels as far as Virginia.

The ship is based with Russia's northern fleet on the North Sea but had stopped over in Cuba before conducting its patrol along the Atlantic Coast and is expected to return there following its latest mission.

The vessel is outfitted with a variety of high-tech spying equipment and is designed to intercept signals intelligence.

The official said that the US Navy is "keeping a close eye on it".

The Leonov is a Vishnya-class spy ship, as is a Russian vessel that trailed the US ship that encountered close-flying Russian aircraft in the Black Sea on February 10.

The USS Porter was sailing in the Black Sea when it had three encounters with the Russian aircraft.

They were deemed unsafe and unprofessional because of how close the Russian planes flew to the American destroyer. The Pentagon later released pictures of the encounter.