"Our military is maintaining thorough preparations against the possibility of North Korea carrying out a nuclear test… We are keeping particularly close attention to the possibility because today marks the founding anniversary of the North's armed forces," South Korean Defense Ministry spokesman Moon Sang-gyun said as quoted by the Yonhap news agency.
According to the spokesman, Seoul has detected signs of Pyongyang's preparations for the nuclear test.
The official, however, noted that North Korea may conduct a nuclear test at any time as it maintains technical readiness to do so.
In early January, North Korea successfully carried out a hydrogen bomb test, putting a satellite into orbit a month later, in violation of UN Security Council resolutions. In March, North Korea conducted multiple short and medium-range rocket launches.
In response to North Korea's recent activities, South Korea and the United States have launched large-scale military drills in the region. The exercises, expected to last through April 30, include rehearsals of strikes on North Korea’s missile and nuclear facilities in case of war. Pyongyang has labeled the drills as provocation.