A Russian spy ship has been spotted in the Irish Sea off the north Dublin coast.

The Yantar is reportedly being monitored by the Irish Naval Service.

It's been seen around 60 kilometres off the east coast in the past few day.

Security and Defence Analyst Declan Power says it's in the area to survey undersea infrastructure for the Russian military.

“The listed function is scientific and oceanic and hydrographic surveys and things of that nature,” he said. “But it has been widely accepted in the western European security community that the Yantar’s job is to survey under sea areas with a view to mapping critical infrastructure for Russian military intelligence.”

Mr Power said that this information is incredibly valuable to Russian forces.

"It is incumbent on Russian armed forces to update themselves," he said.

"So that if hostilities in Ukraine broadened and turned into a wider confrontation within Europe, that there would be a number of designated targets that they would strike to degrade western Europe's options, and to deny them for use in any shape or form."

The ship is also being watched by the US and UK.