A Russian spy ship which has been "loitering" off the US east coast this week is capable of intercepting sensitive communications and underwater signals.
The Cold War-era SSV-175 Viktor Leonov warship is rigged with high-tech electronic spying equipment that can monitor and collect data on US Navy sonar.
The intelligence-gathering vessel is also armed with anti-aircraft missiles and guns in the event of an attack or in case the crew needs to defend themselves from a threat.
American officials have downplayed the spy ship's presence in international waters, where it was just 30 miles from a major US submarine base on Wednesday.
With a crew of about 150 to 200 military personnel, the 310ft Viktor Leonov can reportedly transmit data back to superiors via onboard antennae linked to satellites orbiting earth.
For self-defence the ship - along with six other similar Vishnya class spy vessels - is said to be armed with two AK-630 rapid-fire guns and two missile launchers.
After it was launched in 1988 it patrolled the Black Sea before being transferred to Russia's northern fleet, based in the Barents Sea in the Arctic.
It was named after the Russian sailor and war hero who was celebrated for victories against German and Japanese forces during World War II.
US officials have been keeping a close watch on the Viktor Leonov during its first Atlantic mission since US President Donald Trump was elected.
The ship was 30 miles south of Groton, Connecticut, where the New London submarine base is located, on Wednesday.
Grotton is known as the "home of the submarine force" and is the primary east coast submarine base for the US.
A US official told Fox News that the ship's position also put it just south of Montauk on the eastern tip of New York's Long Island.
The official said the Viktor Leonov was "loitering" in international waters.
On Tuesday the ship was spotted just 70 miles from the coast of Delaware.
Its position on Wednesday was the furthest north it has ever travelled up the US eastern seaboard, Fox News reported.
Two years ago it was seen lurking near a submarine base in Kings Bay, Georgia, where the US Navy keeps submarines armed with Trident missile nuclear weapons.
In January 2015 the Viktor Leonov was docked in Havana as Cuba and the US held historic talks to end a freeze on diplomatic relations.
At the time US officials said the ship's presence was legal and nothing out of the ordinary.
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Meanwhile officials at the Pentagon believe the ship will eventually sail south along the US coast and return to the Caribbean, Fox News reported.
In recent weeks it has crossed the Atlantic and stopped in Jamaica as part of a journey that had been planned for months.
US Senator Chris Murphy, a Democrat from Connecticut, expressed concern over the ship's presence.
He wrote on Twitter: "Russia is acting like it has a permission slip to expand influence, test limits of reach. Questions are obvious: does it, and if so, why?"
There have been a number of provocations involving Russia in recent years.
Last Friday four Russian jets flew past a US Navy destroyer, the USS Porter, in the Black Sea, ignoring radio calls from the ship.
The US believes Russia has secretly deployed two battalions of SSC-X-8 cruise missiles, a move that would violate a 1987 treaty.
US-Russia relations have been under intense scrutiny following Trump's victory over Democratic challenger Hillary Clinton last November.
Earlier this week Trump's national security adviser, Michael Flynn, resigned after just three weeks on the job as it emerged that he discussed US sanctions on Russia with Moscow's ambassador to the United States before the president took office and later misled Vice President Mike Pence about the conversations.
Flynn was seen in Moscow as a leading advocate of warmer ties with Russia.
A member of Trump's administration said the president knew for weeks that Flynn had misled the White House about his contacts with Russia but did not immediately force him out, Reuters reported.
Trump has suggested there is a media conspiracy and denied the notion of a "Russian connection" in response to a New York Times report which said members of his presidential campaign had contact with Russian intelligence officials.
Trump tweeted on Wednesday: "This Russian connection non-sense is merely an attempt to cover-up the many mistakes made in Hillary Clinton's losing campaign."
The Kremlin has also denied the reports.