South Korea, Japan and the United States today began a joint naval exercise denounced by North Korea as a reckless provocation. Seoul's defence ministry said the two-day drill involving destroyers, supply ships and helicopters would practise humanitarian operations such as search and rescue missions. A defence ministry spokesman said the exercise is being held in international waters south of South Korea's Jeju island. North Korea has said the three-nation exercise threatened to bring a new cloud of war to Northeast Asia.