A cargo ship that smashed into a US military chartered oil tanker off the northeast coast of England on Monday was carrying sodium cyanide, according to the maritime intelligence company and shipping journal Lloyd’s List.

U.K. police have opened a criminal investigation into a collision between two ships in the North Sea and have arrested a man on suspicion of manslaughter.

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.

A tanker carrying jet fuel for the U.S. military was hit by a container ship off northeast England on Monday, with the collision igniting a blaze on both vessels, causing multiple explosions and forcing both crews to abandon ship.

U.S.-based maritime management firm Crowley, which operates the Stena Immaculate, said the tanker “sustained a ruptured cargo tank containing Jet-A1 fuel,” when the container ship struck it, triggering a fire and “multiple explosions onboard,” with fuel released into the sea. It said all 23 mariners on the tanker were safe and accounted for.

The U.S. tanker that collided with a Portugese-flagged cargo ship Monday in the North Sea is still burning. Britain's coast guard says 36 crew members were rescued and brought to shore after the crash,