AN elite North Korean suicide squad of human torpedoes may have been involved in the sinking of a South Korean ship in mysterious circumstances.

South Korea's Defence Intelligence Command had alerted the Navy weeks ahead of the sinking that North Korean suicide squads were being deployed, according to reports in Seoul, Sky News reports

The "Human torpedo" squads were said to involve small submarines, Sky News reports.

They are navigated so close to the target that their torpedoes or explosives blow up both target and the attackers.

They can also be timed to explode while the attackers escape from the vessel, the mass-circulation South Korean newspaper Chosun Ilbo reported.

The attack by North Korea on the 1200-tonne Cheonan claimed the lives of more than 40 sailors and was in retaliation for an earlier naval defeat, the report added.

"It is the military intelligence's assessment that the North attacked with a heavy torpedo," a military source was quoted as saying by the news agency Yonhap.

"The military intelligence has made the report to the Blue House - the Presidential residence - and to the Defence Ministry immediately after the sinking of the Cheonan that it is clearly the work of North Korea's military," the source added.

South Korea now plans to raise the front half of the Cheonan, which went down near a disputed sea border with North Korea.

It will issue its verdict on the cause of the explosion that sank the warship after that.

If Pyongyang did carry out the attack it would be the deadliest confrontation between the two countries since the Korean War ended in 1953.

The North has denied it had anything to do with the sinking.

Read more on this story at Sky News.