SEOUL (AFP) - North Korea on Tuesday ruled out any apology over the 2010 sinking of the South Korean navel corvette Cheonan, and demanded Seoul lift sanctions imposed after the incident in which Pyongyang has always denied involvement.

Two days ahead of the fifth anniversary of the sinking, in which 46 South Korean seamen died, the North's top military body, the National Defence Commission (NDC), condemned Seoul's steadfast insistence on the "cock-and-bull" idea that Pyongyang was responsible.

The Cheonan was carrying 104 personnel when it sank near the disputed Yellow Sea maritime border between North and South Korea on March 26.

A South Korean-led investigation involving a team of international experts concluded it was sunk by a North Korean submarine torpedo.

Despite Pyongyang's heated denials, Seoul responded with the so-called "May 24 measures" - which amounted to an effective trade embargo on North Korea which remains in place today.

South Korea has insisted it will only consider lifting the sanctions after the North acknowledges its responsibility and apologises.

The NDC statement on Tuesday demanded the immediate end of the trade embargo, arguing that it had been "cooked up under the absurd pretext of the ... fictitious story" of North Korean involvement in the Cheonan sinking.

"The South should clearly understand that its sophism that 'apology' and 'expression of regret' have to precede the lifting of the 'step' can never work," a spokesman for the NDC's policy department said in the statement carried by the North's official KCNA news agency.

Calling for an apology in such circumstances amounted to an "intolerable mockery" of the North's dignity, the spokesman said.

Some influential South Korean business leaders and politicians have also called for the May 24 measures to be lifted, but President Park Geun Hye's administration has held firm to the condition of a sincere apology.

A 2013 documentary by the left-wing South Korean director Chung Ji Young, Project Cheonan, stirred heated debate by exploring alternative explanations for the sinking, including suggestions that the vessel might have hit a reef or collided with an unidentified submarine.

The Cheonan incident and the trade measures imposed by the South triggered a dangerous surge in cross-border tensions.

In November 2010, the North shelled a South Korean border island, killing four people including two civilians and sparking brief fears of a full-scale conflict.