Kim Yong-chun said live-fire exercises conducted by South Korea near the border were a preparation for war with the North.
The drill is one of the largest in South Korea’s history, involving tanks, helicopters and fighter planes.
Tension has been high since North Korea shelled the South’s Yeonpyeong island last month, killing four South Koreans.
South Korean President Lee Myung-bak has promised immediate retalation to any further Northern attack.
The South Korean army acknowledged that the drill was aimed to display its firepower.
Although the South has conducted 47 military drills this year, this is the largest winter live-fire exercise ever conducted on land.
The North earlier branded Seoul’s exercises “warmongering” but until now had not threatened the South with any retaliation.