SEOUL - South Korea's Defense Ministry on Tuesday warned of a "surprise" nuclear test of the Democratic People's Republic of Korea (DPRK) citing increased activity in its main underground test site.

Defense Ministry spokesman Kim Min-seok told a routine press briefing that a lot of activity has been detected in and around the Punggye-ri test site in the northeastern DPRK where its third test was conducted in February last year.

He declined to elaborate on what activities are being made near the test site, citing an intelligence sharing pact with the United States.

"Our military is thinking of possibilities that North Korea (DPRK) may stage a nuclear test by surprise in the short term and that pretend to conduct a test as seen in past cases," said the spokesman.

Kim said verbal threats have been heard recently from the DPRK, declining to unveil where it got sources. Among the bellicose rhetorics were "ready to take next steps that enemies can never think of" and "a great thing will take place before April 30."

The DPRK has entered a phase of carrying out a surprise nuclear test on short notice from its leadership at any time, Kim said.

On Monday morning, the ministry launched a special task force with the Joint Chiefs of Staff to step up efforts to monitor and brace for possible DPRK nuclear detonation.

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