N Korea bans navigation in Yellow Sea: Agency

North Korea has prohibited sea vessels from navigating in the Yellow Sea, prompting South Korea to monitor the region for possible signs of a provocation.     

Although North Korea routinely sets up entry-prohibited areas in the western waters of the sea for military training purposes, the latest ban is unusually long in duration, and will last nearly two months until the end of July, Yonhap News Agency reported Monday, quoting intelligence sources.     

"The authorities, are keeping watch over the region, believing the ban could be a possible sign that there could be a provocation", an intelligence source was quoted as saying by the news agency.     

However, Defence Ministry spokesman won Tae Jae declined to confirm the news report on the North Korea's ban on navigation in the Yellow Sea.     

Meanwhile, South Korea's military is on a heightened alert after the North Korea's underground nuclear test and a subsequent series of short-range missiles firings off its east coast last week.     

The sources could not confirm exactly when the ban was put in place, but mentioned the entry ban applies to "central and northern parts" of the Yellow Sea, the sources said.     

North and South Korean navy vessels had deadly skirmishes in 1999 and 2002 near the Northern Limit LIne, the de facto western maritime border.