Earlier on Monday, South Korean media quoted a source from South Korea’s government, which said that North Korea has declared the “introduction of a state period of a hazardous situation in the Sea of Japan,“ suggesting that more missile launches are possible in the area before the US defense chief visits Seoul this week.
"North Korea has not notified the International Maritime Organization and neighboring countries of its declaration of the no-fly, no-sail zone," South Korean Defense Ministry Vice Spokesman Nah Seung-yong said at a regular briefing.
"The North might have done that internally for the safety of its people on the East Coast," he added.
"South Korean and the US intelligence authorities have been closely monitoring their moves around the clock," he said.
North Korea watchers, however, speculate that the chances are high that Pyongyang will take a provocative step, especially as US Secretary of Defense Ashton Carter plans to start a three-day visit to South Korea on Thursday. The visit is part of a series of planned trips to the region during his first year as Pentagon chief.
Next week will also mark the late leader Kim Il-sung's 103th birthday. He was the country's founder and the grandfather of the current leader, Kim Jong-un.