North Korea to launch ISIS-style terror attacks on South Korea warns spy chief

North Korean leader Kim Jong Un has ordered preparations for launching ISIS-style terror attacks on South Korea, Seoul's spy agency claims.

The warning comes as tensions between the rival nations grow after Pyongyang's recent nuclear test and rocket launch.

In a private briefing to ruling Saenuri Party members, the National Intelligence Service said the North's spy agency has begun work to implement the order to "actively muster capabilities" to carry out cyber and other attacks on South Korea,

North Korea has a history of attacks on South Korea, such as the 2010 shelling on an island that killed four South Koreans and the 1987 bombing of a South Korean passenger plane that killed all 115 people on board.

During the briefing, the NIS said the attacks could target anti-Pyongyang activists, defectors and government officials in South Korea, according to a Saenuri official who was present.

Terror attacks on subways, shopping malls and other public places could also happen, he said.

The official quoted the NIS as saying North Korea could launch poisoning attacks on the activists and defectors, or lure them to China where they would be kidnapped.

The current North Korea stand-off is not expected to calm down soon, as Seoul and Washington are discussing deploying a sophisticated US missile defence system in South Korea that Pyongyang warns would be a source of regional tension.

The allies also say their upcoming annual military drills will be the largest ever. The North says the drills are preparation to stage an invasion.

The US on Wednesday flew four stealth F-22 fighter jets over South Korea and reaffirmed it maintains an "ironclad commitment" to the defence of its Asian ally.

Last month, it sent a nuclear-capable B-52 bomber to South Korea following the North's fourth nuclear test.

Foreign analysts say the North's rocket launch and nuclear test put the country further along its quest for a nuclear-armed missile that could reach the US mainland.

Meanwhile, top scientists have said that recent nuclear tests carried out by North Korea could trigger a nearby volcano to erupt.

Experts from Yonsei University in Seoul claim the pressure caused by a nuclear bomb exploding underground could affect the magma chamber of a volcano – causing an eruption.

"An underground nuclear explosion test near an active volcano constitutes a direct threat to the volcano," Hong Tae-kyung, a professor of seismology said.