North Korea today threatened to launch a "sacred" nuclear war against South Korea if it is attacked.
The warning came as Seoul staged military exercises that have raised already high tensions on the peninsula.
The remarks seemed aimed at revving 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 is "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 has been sparked by South Korea's staging of live-fire drills on Yeonpyeong Island, which was shelled by the North's artillery on November 23. Four South Koreans were killed.
North Korea has said it shelled the island because South Korea fired artillery into its territorial waters first.
South Korea has countered that it fired artillery away from North Korea as part of routine drills.
Earlier today, 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 media has called the drills "provocative" and "offensive."
The two Koreas are still technically at war because their 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 artillery and fighter jets zoomed by to drop bombs today, signalling South Korea's determination to demonstrate its military strength.
The boom of cannons echoed through the valley, and the hills erupted in smoke at training grounds in mountainous Pocheon about 20 miles (30 kms) 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-ever wintertime air and ground firing exercises in terms of the number of weapons mobilised and fired.
New Mexico Governor Bill Richardson warned in an interview that violence could flare anew between the two rivals if the South continues its drills and the North abandons its stated intention of refraining from retaliation.
Exactly one month ago, routine South Korean live-fire drills from Yeonpyeong Island in the Yellow Sea triggered a shower of North Korean artillery that killed two marines and two construction workers. It was the first military attack on a civilian area since the Korean War.
North Korea, which claims the waters around the South Korean-held island lying just seven miles (11 kms) from its shores as its territory, accused the South of provoking the exchange by ignoring Pyongyang's warnings against staging the live-fire drills near their disputed maritime border.
China - North Korea's only major ally - called again for restraint today.
"The current situation remains highly complicated and sensitive," Chinese Foreign Ministry spokeswoman Jiang Yu told a regular briefing. "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,"
The military tension over the past month has soared, and comes on the heels of the March sinking of a South Korean warship that a Seoul-led international investigation blamed on Pyongyang, but which North Korea denies. Forty-six sailors died.