Seoul's spy service says North Korea is preparing attacks

According to an official, Kim Jong Un's spy agency has begun work to launch cyber and other attacks on South Korea

South Korea's spy agency has told ruling party officials that North Korean leader Kim Jong Un recently ordered preparations for launching attacks on South Korea, in the latest sign of high tensions on the Korean peninsula after the North's recent nuclear test and missile launch.

One official from the Saenuri Party who attended today's closed-door briefing by the National Intelligence Service says Kim's spy agency has begun work to implement his order to "actively muster capabilities" to launch cyber and other attacks on South Korea.

North Korea has a history of attacks against South Korea, but it is impossible to independently confirm what's really happening in the secretive North Korea.

The Saenuri official refused to say whether the briefing discussed how the information has been obtained.

He requested anonymity because he wasn't authorised to speak to media on the briefing.

The spy agency said the attacks could target anti-Pyongyang activists, defectors and government officials.

The comments come a day after four of the most advanced US fighter jets flew over South Korea in a clear show of force against North Korea amid a festering standoff over its nuclear and missile ambitions.

The stealthy, high-tech F-22 planes capable of sneaking past radar undetected landed at Osan Air Base near Seoul after the flyover escorted by other US and South Korean fighter jets.

Pyongyang will likely view the arrival of the planes flown from a US base in Japan as a threat as they are a display of US airpower apparently aimed at showing what the United States can do to defend its ally South Korea from potential aggression from North Korea.

The US military would not say how long the F-22s will be deployed in South Korea.

The United States often sends powerful warplanes to South Korea in times of tension with North Korea. Last month it sent a nuclear-capable B-52 bomber to South Korea after North Korea defiantly conducted its fourth nuclear test.

The international standoff over North Korea deepened earlier this month when Pyongyang ignored repeated warnings by regional powers and fired a long-range rocket carrying what it calls an Earth observation satellite. Washington, Seoul and others consider the launch a prohibited test of missile technology.

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.

South Korea's president on Tuesday warned North Korea faces collapse if it doesn't abandon its nuclear bomb program, an unusually strong broadside that is certain to infuriate Pyongyang.