The North's military said it fired 10 rocket artillery rounds after a South Korean navy ship violated the NLL and fired warning shots "on the pretext of tracking down an unidentified ship," according to state media."We once again urge North Korea to immediately cease consistent provocations and accusations which harm the peace and stability of the Korean peninsula as well as the international community," the JCS said in a statement.In recent weeks, North Korea launched short-range ballistic missiles and hundreds of artillery rounds off its east and west coasts on several occasions in protest over the South's military activities.South Korea's troops kicked off their annual Hoguk defence drills last week, designed to run until Oct. 28 and boost their own and combined ability with the United States to counter the North's nuclear and missile threats.As part of the programme, South Korean naval forces said on Monday that they would stage four-day exercises off the west coast, bringing together about 20 warships, including their Aegis-equipped destroyer and U.S. assets such as Apache attack helicopters and A-10 strike aircraft."