North Korea is showing no signs yet of any immediate ballistic missile launch, Seoul's defense ministry said Monday, amid growing concerns about the possibility of an additional provocation by the communist nation.

On Friday, the North test-fired four short-range missiles presumed to be KN-02 ground-to-ship ones into the West Sea following the test-firing of a single projectile the previous day, according to Seoul's Joint Chiefs of Staff.  

"No concrete, specific signs have been detected as I've just checked (the latest developments)," defense ministry vice spokesman Nah Seung-yong said at a regular briefing, when asked if there was any unusual move in the secretive country.

"South Korean and the U.S. intelligence authorities have been closely monitoring their moves around the clock," he added.

The official dismissed a news report that the North designated a no-fly and no-sail zone in the East Sea, which could be an indication of an immediate ballistic missile launch.

"North Korea has not notified the International Maritime Organization and neighboring countries of its declaration of the no-fly, no-sail zone," Nah said. "The North might have done that internally for the safety of its people on the East Coast."

North Korea watchers, however, say chances are high for Pyongyang to take a provocative step, especially as U.S. Secretary of Defense Ashton Carter plans to visit Seoul later this week. It will also mark late leader Kim Il-sung's 103th birthday next week. He was the country's founder and the grandfather of the current leader Kim Jong-un. (Yonhap)