South Korea reportedly used howitzers, mortars and attack helicopters in live-fire exercises on Monday near the country's heavily armed Yellow Sea border with North Korea.
Pyongyang has described the military drill as a provocation, according to CNN, which indirectly cited a bulletin from the Secretariat of the Committee for the Peaceful Reunification of Korea: "This is a very dangerous play with fire to ignite a war against the North as it is a clear declaration of war against it."
The bulletin was reported by Pyongyang's state-run Korean Central News Agency, CNN wrote.
The drill took place Monday on islands off the west coast of the Korean peninsula, where tensions have flared in the past.
Seoul notified the North of the one-day "routine" drill, Agence France Presse reported, adding that they began the exercise at about 10 a.m. and halted them before noon.
However, according to the New York Times, the North still warned South Korean villagers in the area to evacuate or take cover.
It also vowed "merciless retaliatory strikes" if any shells land in waters claimed by Pyongyang, saying that Seoul "should not forget the lesson" of the bombardment of Yeonpyeong island in November 2010, which killed four South Koreans, AFP wrote.
That attack was in retaliation for a live-fire exercise which dropped shells into waters claimed by the North, Pyongyang said.
"If the puppet warmongers pre-empt reckless firing despite our warning, they will not escape punishment thousands-fold severer" than the shelling of Yeonpyeong Island, the reunification committee bulletin said, identifying the "warmongers" as South Korea and the US.
The Times wrote that the drill came as the North Korean regime was "going through a sensitive power transition" following the death of leader Kim Jong Il.
His son and heir, Kim Jong-un was also consolidating his grip on power in Pyongyang, and analysts were "closely watching how Kim’s attempts to assert his own authority ... might affect North Korea’s relations with its neighbors."