LONDON (Reuters) - Most of the jet fuel onboard the U.S.-flagged tanker Stena Immaculate that was hit by a container ship in a collision off Britain's coast remains contained and only two of the vessel's 18 fuel tanks have leaked, owner Stena Bulk said on Wednesday.

The captain of the Solong cargo ship who was arrested after crashing into an oil tanker off the English coast is a Russian national, the vessel’s owner said Wednesday, as maritime experts search for answers.

The tanker that was hit at anchor off the coast of England in the North Sea was under contract by Military Sealift Command in support of the Defense Logistics Agency, USNI News has learned. The U.S.-flagged MV Stena Immaculate was at anchor when Portugeuse-flagged container ship MV Solong struck the tanker at about 5:48 a.

U.K. police say the Solong cargo ship's captain, identified by the vessel's owner as a Russian national, was detained on suspicion of negligent manslaughter.

Fears of an environmental disaster eased on Wednesday, two days after a container ship ploughed into a stationary U.S. fuel tanker off northeast England, as the vessel's owner said the detained captain was a Russian national.

On Monday, in a tragic incident, a Portuguese-flagged cargo vessel called Solong, carrying toxic chemicals, crashed into a US-flagged tanker carrying jet fuel for the US Army off the UK coast. According to the reports quoting Solong’s owner,