Kim Jong Un (Reuters)

North Korea warned today that the US will “pay dearly” if it relists Pyongyang as a state sponsor of terrorism following the murder of leader Kim Jong-Un’s half-brother in Malaysia last month.

Kim Jong-Nam, 45, was killed on February 13 at a crowded Kuala Lumpur airport in an attack with VX nerve agent, which is considered a weapon of mass destruction.

Seoul has said from the start that the isolated North is behind the Cold War-style assassination.

South Korean and Japanese media, citing diplomatic sources, have since reported that the US has been mulling placing the North back on its terror list, which includes Iran and Syria.

“The US will keenly realise how dearly it has to pay for its groundless accusations against the dignified” North if it relists it, the regime’s foreign ministry spokesman told state-run newswire KCNA.

The spokesman maintained that Pyongyang opposed “all forms of terrorism” and accused the US of trying to tarnish its reputation.

“Gone are the days when the US could stigmatise at random to oppress those countries incurring its displeasure, while having the world under its control,” the official added.

The nuclear-armed North was first designated a state sponsor of terrorism in 1987 when its agents bombed a South Korean plane killing all 115 on board.

But it was taken off the list in 2008 after Pyongyang took steps toward freezing its nuclear facilities.

However, since then the North has resumed its activities, conducting four atomic tests and numerous missile tests despite the fact that they are banned under several UN Security Council resolutions.

The North has denied any involvement in Kim Jong-Nam’s murder, accusing the South, the US and Malaysia of a “smear campaign”.

Two women, one Vietnamese and one Indonesian, have been arrested over the murder.

The only North Korean to have been detained, Ri Jong Chol, was released this week due to lack of evidence.

Ri has denied any role in the assassination and accused of Malaysian police trying to frame him with “fabricated evidence” to defame the North.