The drills were taking place as US and North Korean envoys prepared to meet on Wednesday in Beijing to discuss a recent nuclear deal.
The Associated Press was among the media allowed to watch the drills along North Korea's southwestern coast on Monday.
Troops were seen firing automatic rifles and handguns at a target bearing the name of South Korean President Lee Myung-bak.
Artillery gunners aimed their weapons towards Paekryong island, which lies in disputed waters where four South Koreans were killed in 2010.
Colonel General Pyon In Son, Commander of 4th Corps of the Korean People's Army, who appeared to be leading the exercise said at the time of Yonpyong island shelling incident "only a few guns were fired."
"But since Lee Myung Bak's treacherous group want to provoke us this time, thousands of guns of our corps will open fire at the same time, turning the enemy into a sea of fire, and none of the treacherous group will be left alive," he said.
Other troops practised martial art moves and chanted: "Beat rabid dog Lee Myung Bak to death"
North Korean leader Kim Jong Un visited the heavily armed border with rival South Korea and ordered troops to be on high alert, state media reported on Sunday, just days after Washington and Pyongyang agreed to a nuclear deal after years of deadlock.
On Sunday, tens of thousands of North Koreans rallied in Pyongyang, vowing to topple South Korean President Lee Myung-bak, who ended a no-strings-attached aid policy to the North when he took power in 2008, instead linking assistance to nuclear disarmament.
The US and North Korea announced last week that Washington had agreed to provide 240,000 metric tons of food aid in exchange for a freeze of North Korea's nuclear activities.
A US envoy is scheduled to meet with North Korean officials in Beijing on Wednesday to discuss the distribution of food.
The deal is seen as a first step toward resuming six-nation nuclear disarmament-for-aid talks suspended in 2009, and a tentative move toward improving the tense relationship between the wartime foes.
The six-nation talks involve the two Koreas, the US, China, Russia and Japan