A large fuel oil slick thought to have leaked into the Celtic Sea during a Russian refuelling incident is heading to the coasts of Ireland and Wales.
The UK coastguard estimates up to 1,000 tonnes may be on the water, but Russia denies the spill is on that scale.
Irish coastguards said the spill, 50 miles (80km) off of west Cork, covered 2.8 miles by 3.1 miles around a Russian aircraft carrier and a tanker.
It was first spotted by aerial pollution surveillance on 14 February.
Samples from the spill have been taken for analysis, the Irish coastguard said, and the Russian Embassy has been asked by the Irish government to supply data about oil on its ships.
Aerial monitoring was still being carried out by Irish and British maritime agencies, reports said.
The Russian navy said it was carrying out an internal investigation, but could not confirm how the oil came to surround its vessels or whether its refuelling operations had caused the spill.
There are two refuelling tankers, one aircraft carrier, one Russian tug, a Russian destroyer, a British destroyer and an Irish naval vessel in the area.
The Irish coastguard said the slick was breaking up and was spreading over a larger area and moving eastwards about 30 to 40 miles off the coast.
The majority of the oil is expected to remain on the surface, it said in a statement.
“The residual oil remaining is expected to develop into tar balls.
“Depending on weather conditions these may end up on the Irish south-east coast in approximately 16 days time and also impact on the Welsh coastline.
“At this point it is too early to predict accurate volumes.”
Local authorities said they were preparing to deal with any oil which reached the shore, while a tug was being sent to the slick to see if the oil could be recovered at sea.