South Korea-US military drill shadowed by North Korea threats

Tens of thousands of South Korean and US troops began a military exercise simulating an all-out North Korean attack today, as Pyongyang issued bellicose threats of pre-emptive nuclear strikes in retaliation.

The two-week annual Ulchi Freedom exercise is largely computer-simulated, but still involves around 50,000 Korean and 25,000 US soldiers.

The drill always triggers a spike in tensions on the divided Korean peninsula, and this year it coincides with particularly volatile cross-border relations following a series of high-profile defections.

As the exercise began, South Korean President Park Geun- Hye said the defections signalled domestic turmoil in Pyongyang that could cause North Korea to lash out.

"It is increasingly possible that North Korea may undertake various terror attacks and provocations... To block internal unrest, prevent further defections and create confusion in our society," Park told a cabinet briefing.

Her comments came a day after the Unification Ministry in Seoul urged all citizens to be on guard against possible North Korean assassination attempts on defectors and anti-Pyongyang activists in the South.

Park said the South Korean military was on high alert and would "vigorously strike back" in the event of any hostile action.

Ulchi Freedom plays out a full-scale invasion scenario by nuclear-armed 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 would result in the source of the provocation being turned "into a heap of ashes through Korean-style pre-emptive nuclear strike," the spokesman said.

Seoul voiced regret at the aggressive tone of the KPA statement, with the Unification Ministry urging the North to Korea "break away from provocative actions."

Pyongyang has made similar nuclear strike threats in the past, but actual retaliation to South Korea-US military drills has largely been restricted to firing ballistic missiles into the sea.

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.