South Korea begins live-fire exercises despite threats from the North Military officials said the "routine" drill, their second this year, would involve self-propelled howitzers, Vulcan cannon, mortars and Cobra attack helicopters. The North said that attack was in retaliation for a live-fire exercise which dropped shells into waters which Pyongyang considers part of its maritime territory. The 2010 attack briefly sparked fears of war and triggered a major South Korean military build-up on the islands. Seoul has vowed to hit back harder, using air power, for any fresh strike. Early Monday, Pyongyang repeated threats of possible retaliation. "If the puppet warmongers pre-empt reckless firing despite our warning, they will not escape punishment thousands-fold severer than the past Yeonpyeong Island shelling," said a statement issued in the name of an official body called the Committee for the Peaceful Reunification of Korea. Pyongyang has taken a hostile tone towards Seoul since Kim Jong-un, the youngest son of the late leader Kim Jong-il, took over following the death of his father in December. South Korea says the drill is a regular monthly exercise designed to maintain combat-readiness in the flashpoint border region. Officials said residents of the front line islands would be advised to relocate to safe zones before the firing begins.