SEOUL – Tens of thousands of South Korean and US troops began a military exercise simulating an all-out North Korean attack today, as Pyongyang threatened a pre-emptive strike on forces participating in the drill.

The two-week annual Ulchi Freedom exercise is largely computer-simulated, but still involves 50,000 Korean and 30,000 US soldiers.

Ulchi Freedom plays out a full-scale invasion scenario by North Korea and both Seoul and Washington insist it remains purely defensive in nature.

Pyongyang views the drill as wilfully provocative and the Korean People’s Army (KPA) issued a statement this morning, threatening a military response to what it described as a rehearsal for a surprise nuclear attack and invasion of the North.

North Korea’s frontline units were "fully ready to mount a preemptive retaliatory strike at all enemy attack groups involved," said a spokesman for the KPA General Staff.

The slightest violation of North Korea’s territorial sovereignty during the military drill would result in the source of the provocation being turned "into a heap of ashes through Korean-style preemptive nuclear strike," the spokesman said.

Pyongyang has made similar threats in the past, but analysts say the risk of an unintended incident escalating into a military clash is higher this year given the lack of direct communication between the two Koreas.

As tensions rose in the wake of North Korea’s fourth nuclear test in January, Pyongyang shut down the two existing hotlines with South Korea - one used by the military and one for government-to-government communications.

And last month it severed its only direct communications link with the US when it shut down the so-called "New York channel" which had previously served as a key point of contact between North Korean and US diplomats at the United Nations. – AFP