A North Korean navy patrol boat has briefly crossed the western maritime border with South Korea. The office of the Joint Chiefs of Staff said it is the seventh such violation this year. The North Korean patrol boat sailed about eight hundred meters across the border as it was directing North Korean fishing boats operating in the area. But South Korean officials said the fishing boats did not cross the border. The patrol boat stayed in the area for 50 minutes before South Korean navy warships chased it back across the border. South Korea accused North Korea of making 12 brief border violations in the western sea last year. In 19-99, a series of violations by North Korean ships touched off the first naval clash between the two Koreas since the Korean War. One North Korean warship sank and about 30 sailors were believed to have drowned. Several South Korean sailors were slightly wounded.