North Korea accused South Korea Sunday of inventing allegations against it to raise tension and repeated denials of involvement in a deadly ship sinking and a damaging cyber-attack on a bank.

"We strongly urge the group of traitors to own responsibility for faking up the conspiratorial farces doing harm to the fellow countrymen and make an official apology before the nation," the North's top leadership body the National Defence Commission (NDC) said, referring to the South's leaders.

The North has repeatedly denied involvement in the sinking of a South Korean warship near the disputed sea border in March 2010 with the loss of 46 lives.

Last week its defence ministry also denied carrying out a cyber-attack on one of South Korea's largest banks in April, calling the allegations "absurd" and a "farce".

South Korean prosecutors say the North brought down the computer system of the National Agricultural Cooperative Federation by hacking into an official's laptop and operating it remotely as a "zombie computer".

Sunday's NDC statement via the North's official news agency repeated those denials.

The South, citing a multinational investigation, said a North Korean torpedo sank the warship and put what it said was a salvaged portion of the torpedo on display.

The North said its neighbour cooked up the story as part of what it calls a policy of confrontation designed to ensure a continuing US military presence.

The NDC, which is chaired by leader Kim Jong-Il, said the cyber-attack claim followed recriminations between Seoul's presidential palace and the ruling party over a by-election setback.

It said further allegations may be "orchestrated as long as the group of traitors is working hard to stoke confrontation between the North and the South".