South Korean officials and international experts say the likelihood of North Korea conducting a fifth nuclear test in the near future has increased because of a failed missile launch yesterday which was an embarrassing setback for leader Kim Jong Un.
North Korea holds a ruling Workers Party congress in early May, at which Kim is likely to trumpet his achievements in building up Pyongyang's weapons prowess.
South Korean officials and weapons experts say he will be keen to go into the congress with a show of strength, and not a failed rocket launch.
A senior South Korean official says North Korea is capable of conducting an additional nuclear test at any time if Kim gives the go-ahead.