The army and air force joint drills mobilized some 800 troops and 105 types of modern weaponry, including K9 self-propelled howitzers, attack helicopters, multiple-launch rocket systems and six fighter jets Thursday, according to South Korea's Defense Ministry.
''The drills aim at checking preparedness to deliver strong retaliation against the enemy's provocation,'' a statement said.
The drills at Pocheon in Gyeonggi Province are the latest in a series South Korea has held in the wake of the North's artillery attack in late November on a western border island that left four South Koreans dead.
The North's attack was the deadliest on a civilian target since the 1950-1953 Korean War.
Meanwhile, President Lee Myung Bak visited a frontline military army unit in Gangwon Province on Thursday to check defense preparedness, according to the presidential office.
''Our armed forces should maintain impregnable defense and also launch merciless counterattack when they come under a surprise attack,'' Lee said during his visit to the army unit, according to a pool report.
Lee also said he believed being patient with North Korea would bring peace on the Korean Peninsula, but the reality was not so.
On Monday, South Korea conducted a live-fire drill from Yeonpyeong Island, the site of the shelling by North Korea in November.
The South's navy began a four-day maritime exercise off the east coast Wednesday that involves six naval ships and Lynx antisubmarine helicopters.
The drills, about 100 kilometers south of the eastern sea maritime border with the North, aim at beefing up preparedness for possible intrusion by submarines and patrol boats.