North Korea is capable of conducting a fifth nuclear test at any time, Seoul's Unification Ministry said Monday, amid signs of continued activities in the communist state's nuclear experiment site.

"We believe that (the North) is able to carry out a fifth nuclear test immediately," ministry spokesperson Jeong Joon-hee said during a regular briefing, stressing that the government is preparing for "all possibilities."

Seoul officials have said that Pyongyang remains "technically ready" to conduct another underground atomic experiment, and that it would push ahead with another test based upon a "political" decision.

Last week, Pyongyang threatened to conduct another test of nuclear warheads and ballistic missiles, further heightening tensions on the Korean Peninsula.

The threat is seen as an angry response to the ongoing South Korea-U.S. military drills and the recent adoption of fresh U.N. Security Council sanctions on the communist regime for its nuclear test in January and long-range rocket test in February.

38 North, a U.S.-based website specializing in North Korea news, has said that there has been "continued activity" at the North's main nuclear experiment site in Punggye-ri in the northeastern part of the country. It said that it is highly likely that the site is capable of "supporting additional tests at any time."

Responding to the report, the defense ministry's spokesman Moon Sang-gyun said, "North Korea is maintaining a condition in which they could do a nuclear test when its leadership makes a decision."

Taking that into consideration, the military is keeping close tabs on the situation and making itself ready in collaboration with the intelligence agencies of South Korea and the United States, he added.  (Yonhap)