South Korea and the United States launched on Monday two-week joint drills involving thousands of troops, under the name “Key Resolve”, following a week of escalating tensions on the Korean peninsula.

South Korea and the United States launched on Monday two-week joint drills involving thousands of troops, under the name “Key Resolve”, following a week of escalating tensions on the Korean peninsula.

North Korea had condemned the annual joint maneuvers as a provocative invasion rehearsal and announced that – effective Monday - it was scrapping the 1953 armistice and voiding non-aggression treaties signed with the South.

The South's Unification Ministry confirmed that the North appeared to have carried through on another promise to cut a telephone hotline between Pyongyang and Seoul.

"The North did not answer our call this morning," a ministry spokeswoman said. The hotline was installed in 1971 and the North has severed it on five occasions in the past -- most recently in 2010.

In a dispatch late Monday from its official news agency KCNA, North Korea restated its view that the armistice, "which has existed for form's sake, would be completely invalid from March 11".

The US-South Korean war games are "bringing the dark clouds of a nuclear war to hang over the Korean peninsula", KCNA added, while vowing that North Korea's armed forces were ready for an "all-out action".

"Key Resolve" is an annual, largely computer-simulated exercise, but still involves the mobilization of more than 10,000 South Korean and 3,500 US military personnel. About 28,500 US troops are stationed in South Korea.