North Korea has reportedly increased activities at its main nuclear test site, South Korea's Defence Ministry has said.
The move has prompted South Korea and the United States to prepare for a new nuclear missile test by Pyongyang.
The announcement came ahead of President Barack Obama's scheduled trip to Japan and South Korea later this week, Fox News reports.
Defense Ministry spokesman Kim Min-seok said the South Korean intelligence had 'detected various types of activities at Punggye-ri', referring to the test site in northeastern North Korea, the report said.
The Korean newspaper Chosun Ilbo, citing a source in the Seoul government, said that observers had noticed 'a very brisk movement of vehicles and people in and around' the site, it added.
