North Korea is readying a fourth nuclear test, but no imminent sign has been detected at its main site in the northeastern tip, South Korea’s defense ministry said on Friday, according to South Korean News Agency (Yonhap). In a parliament briefing before the special security committee on North Korea’s nuclear weapons, South Korea’s Vice Defense Minister Baek Seung-joo spoke of the condition of the Punggye-ri test site in North Korea’s northeastern region as speculation over another nuclear test mounts. The southern tunnel of the underground test site can be used for another explosion at any time, but currently there are no imminent signs for such action, Baek was quoted as saying by participants, Yonhap reported. The western tunnel, where the third explosion took place in February, is currently under construction, Baek said. Pyongyang is expected to acquire 6 km of weapons-grade plutonium by the end of next year if the Yongbyon nuclear reactor continues to operate in the current phase, he noted.