Ireland's RTE channel reported on Monday that two Russian warships had spilled 12 tons of oil into the sea some 400 km (250 miles) off the coast of Ireland, probably while refueling. Other media said up to 400 tons could have been spilled.

"The nature and reasons for the possible pollution will be determined by experts only after a comprehensive probe," said Capt. 1st Rank Igor Dygalo. "It is now absolutely clear that its scope does not correspond to media reports, it [the spill] is not catastrophic and poses no environmental threat to the shoreline."

Although he confirmed that Russian warships had carried out refueling in the region, he ruled out that an emergency situation might have occurred.

Dygalo also said Russian experts were ready to share data and work in conjunction with specialists from other countries to identify the cause of the oil slick.

The Irish authorities have said that "the Irish Coast Guard are in contact with the Russian authorities and are monitoring the spill, which is breaking up," dismissing earlier reports that suggested a collision had occurred between two nuclear-powered ships.

The Friends of the Earth international environmental organization has called for a full investigation into the incident, saying the spill could cause serious damage to marine life.