North Korea has threatened to launch a "sacred" nuclear war against South Korea if it is attacked.
The warning came as Seoul staged military exercises that raised already-high tensions on the peninsula.
The remarks seemed aimed at boosting patriotic spirit on the eve of the 19th anniversary of leader Kim Jong Il's appointment as the supreme military commander.
Defence chief Kim Yong Chun said North Korea was "fully prepared to launch a sacred war" – and would use its nuclear capabilities – if attacked and warned the South against intruding onto even the smallest amount on its territory, according to the official Korean Central News Agency.
North Korea's anger followed South Korea staging of live-fire exercises on Yeonpyeong Island, which was shelled by the North's artillery on November 23. Four South Koreans were killed.
The North says it shelled the island because South Korea fired artillery into its territorial waters first but the South has said it fired artillery away from North Korea as part of routine exercises.
Earlier yesterday, South Korea conducted its largest air-and-ground firing drills near the tense land border in a show of force against North Korea.
The North's state news media called the drills "provocative" and "offensive." The two Koreas are still technically at war because the 1950-53 Korean War ended with an armistice, not a peace treaty.
Earlier, South Korea's president vowed a strong response if North Korea attacks again.
"I had thought that we could safeguard peace if we had patience, but that wasn't the case," President Lee Myung-bak said during a visit to a front-line army base near the Koreas' eastern land border, according to his office. "Our military must ... make unsparing response if it suffers surprise attacks."
Near the Koreas' land border, South Korean tanks fired their guns and fighter jets dropped bombs, signalling South Korea's determination to demonstrate its military strength.
The boom of cannon echoed through the valley and the hills erupted in smoke yesterday at training grounds in mountainous Pocheon about 20 miles from the border. Rockets streamed through the air and slammed into the side of a hill as helicopters fired at targets and F-15 jet fighters dropped bombs.
The drills were the armed forces' largest joint firing exercises this year and the biggest-yet wintertime air and ground firing exercises in terms of the number of weapons mobilised and fired.
The governor of New Mexico in the United States, Bill Richardson, warned in an interview that violence could flare anew if the South continued its exercises and the North dropped its stated intention of refraining from retaliation.
A month ago, routine South Korean live-fire drills from Yeonpyeong Island in the Yellow Sea triggered barrage of North Korean artillery that killed two marines and two building workers.
North Korea, which claims the waters around the South Korean-held island seven miles from its shores as its territory, accused the South of provoking the exchange by ignoring Pyongyang's warnings against staging the drills near the disputed border.
China – North Korea's only major ally – called again for restraint yesterday.
"The current situation remains highly complicated and sensitive," said Jiang Yu, a spokeswoman for the Chinese foreign ministry in Beijing.
"We appeal to the relevant parties to keep calm, exercise restraint, and adopt responsible attitudes and do more to ease the situation and safeguard peace and stability on the peninsula,"