Seven Nigerian men arrested on suspicion of attempting to hijack an oil tanker off the coast of southern England last year will face no further action, UK police said Friday.

Police in the southern county of Hampshire, who have been probing the October incident, said prosecutors made the decision following the emergence of "additional evidence" during the investigation.

"After additional maritime expert evidence came to light, we concluded there was no longer a realistic prospect of conviction and discontinued the case," prosecutor Sophie Stevens said in a statement released by police.

The discovery of the men on the Nave Andromeda oil tanker, who smuggled themselves aboard in the Nigerian city of Lagos, sparked a special forces raid as the vessel passed near the Isle of Wight.

Police arrested them on suspicion of "seizing or exercising control of a ship by use of threats or force" after a mayday call from the 43,000-tonne tanker.

Two of the group had previously been charged and already appeared in court.

The seven will remain detained under immigration powers, according to police.

Detectives had said the men threatened the 22-member crew, forcing them to seek sanctuary in the ship's citadel, from where they raised the alarm.

The Liberian-flagged, Greek-owned vessel, which was six miles (10 kilometres) off the Isle of Wight on England's south coast at the time, was eventually taken to the port of Southampton.

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