Tánaiste and Minister for Foreign Affairs Simon Harris has said that a Russian intelligence-gathering ship has "left our area of interest".
Speaking during a visit to Athlone, Mr Harris said the Defence Forces had been monitoring the vessel off the Irish coast for around 36 hours.
Mr Harris said he has been kept updated on the situation.
It is understood that LÉ Samuel Beckett was dispatched to monitor the Viktor Leonov as it sailed towards Havana in Cuba.
The Naval Service vessel, along with an Air Corps maritime surveillance aircraft, shadowed the ship as it made its way through Ireland's Exclusive Economic Zone.
Attempts were made by the Naval Service to communicate with the ship to establish its purpose in the area but it did not respond.
The Viktor Leonov is part of the Vishnya class of intelligence-gathering ships and usually operates near the east coast of the United States.
These types of vessels can gather information by intercepting communications.
In November, a Russian spy ship was found to be operating near subsea cables in the Irish Sea.
The Naval Service monitored the activities of the Yantar - which has a crew of 60 and is ostensibly an oceanographic research vessel - as part of a multinational intelligence-led operation.
Additional reporting Jackie Fox
