North Korea said Tuesday it was ready to provide torpedo samples to back up its denial of responsibility for the deadly sinking of a South Korean warship.

It said aluminium alloy fragments salvaged by South Korea from the site of the sinking in March "prove, themselves, that the torpedo was not from the North".

North Korean torpedoes are "made of steel alloy material" not the aluminium alloy used in other countries, said the country's top ruling body, the National Defence Commission.

"(North Korea) is still willing to directly hand the steel alloy sample of Juche (self-reliance)-based torpedo" to the United States and South Korea, it said in a statement carried by the official Korean Central News Agency.

The 1,200-tonne Cheonan was split into two on March 26 near the tense disputed border off the west coast, in one of the divided peninsula's deadliest incidents in decades.

The incident plunged cross-border relations to their lowest point in years and sharply raised regional tensions.

The North, in a statement several thousand words long, rejected as the "most hideous conspiratorial farce in history" the findings of a Seoul-led multinational probe.

That inquiry in May concluded that a submarine-launched North Korean torpedo sank the corvette with the loss of 46 lives.

Investigators cited "overwhelming" evidence, including a partial torpedo motor and propeller said to have been dredged from the seabed. They said this matched a type which the North had previously offered for export.

The South announced reprisals including a partial trade cut-off and staged several naval exercises as a warning to the North, some of them in conjunction with the United States.

In September the South reaffirmed the findings in a final report.

Russia sent its own experts to Seoul for an independent investigation but has not made the results public.

The North has demanded the right to send a high-level team to the South to inspect the evidence, including the torpedo part.

The South has rejected the demand, saying the UN Command should handle the case as a serious breach of the armistice that ended the 1950-53 war.

The North, as it has done earlier, disputed the scientific findings of the multinational investigation.

It also cast doubt on the discovery of the torpedo motor and propeller.

"It is nonsensical for them to claim that a civilian fishing boat appeared all of a sudden and netted the propelling body which dozens of warships equipped with sophisticated detecting devices failed to find out in at least 50 days," the statement said.

Citing what it called assertions by some experts, the North also claimed the warship could have broken into two after running aground on rocks.

If the hull had been split by a torpedo, it said, the edges would not have been jagged and the hull would have had fragments embedded in it.

Some South Koreans have also been sceptical about the assertion that a North Korean torpedo sank the ship. Alternative theories have included a grounding and a stray mine.

The South's defence ministry made no immediate comment on the North's fresh claims. The ministry, when releasing its final report, had said it was acting to dispel "groundless suspicions".