North Korea's military threatened Sunday to launch the "severest punishment" against South Korea for staging massive joint war games with the United States this week.
The North's army and people will "deal a merciless counterblow" to the allies "as it had already resolved and declared at home and abroad", a spokesman for the country's army General Staff said in a statement published by state media.
"The military counteraction of (North Korea) will be the severest punishment no one has ever met in the world," he said.
The warning came a day before US and South Korean troops begin the 10-day computerised war games called "Ulchi Freedom Guardian (UFG)".
About 30,000 US soldiers will take part in the exercise, a US military spokesman said, adding an unspecified number of American soldiers based in the United States would join in via computer networks.
Some 56,000 South Korean soldiers will be mobilised for the war games, a defence ministry spokesman said.
In a message posted on a US military website, General Walter Sharp, who heads some 28,500 US troops based in the South, described the exercise as "one of the largest joint staff directed theatre exercises in the world."
A separate security drill involving South Korean government officials and soldiers will be held during the period, Yonhap news agency said.
This week's exercise is one of a series planned by the South -- either alone or jointly with the United States -- in the aftermath of the sinking of a South Korean warship in March.
The North has angrily denied responsibility for the sinking, which killed 46 sailors and sharply raised tensions on the Korean peninsula.
Last month South Korea and the United States held a massive joint naval and air drill in the Sea of Japan (East Sea), which were opposed by Beijing.
A week ago South Korea ended its largest-ever anti-submarine drill including live-fire training near the disputed Yellow Sea border.
The war manoeuvres including the UFG exercise "represent the phase of practical actions aimed at a full-dressed military invasion", the North's spokesman said.
"The more recklessly the warmongers persist in the war rackets as a result of wrong policy option, the faster and deeper they will fall into the grave of self-destruction," he said.
China also issued a warning Friday that a US decision to use a nuclear-powered aircraft carrier in joint drills with the South constitutes a "fresh provocation" to China and its neighbours.
In a commentary published in the official China Daily, Rear Admiral Yang Yi said Washington would "pay a costly price for its muddled decision" to participate in further drills near Chinese territory over Beijing's objection.
Yang also warned it was "inadvisable" to push a country of 1.3 billion people, noting that there was instead wide scope for US-China naval cooperation should Washington choose the route of caution.
Last week, Pentagon spokesman Geoff Morrell said future joint US-South Korea drills would involve the nuclear-powered USS George Washington in the Yellow Sea.
China is North Korea's closest ally and trade partner and Beijing has refused to join in international condemnation of Pyongyang for the sinking of a South Korean warship.