An oil pollution alert has been declared off the southwest coast following an incident in which two Russian military vessels were involved in a fuel spill accident.
The coastguard service says up to 300 tonnes of oil spilled into the sea about 80km south of Fastnet lighthouse and a large oil slick has developed in the area.
In a statement the Department of Transport says the two ships did not collide and that neither of them are nuclear.
They believe the incident may have occurred as a result of a refuelling operation.
The coastguard is in contact with the Russian authorities and is monitoring the spill.
It is not expected that any oil will reach the shore.
Samples of the oil were taken by other boats operating in the area and were transferred to the Shannon-based helicopter.