There are hints that North Korea might carry out another nuclear test soon, South Korea said Tuesday.



There was evidence of "heightened activity" at the nuclear testing ground in north-west North Korea, a spokesman for the Defense Ministry in Seoul said.

The report comes just days before U.S. President Barack Obama is scheduled to visit South Korea. Obama will arrive in Seoul on Friday, after a three-day visit in Japan.



"North Korea may suddenly conduct a nuclear test in a short period of time, or as in previous cases, deceive us with what appears to be a nuclear test," he said.



Pyongyang threatened a "new kind" of atomic test in late March.

North Korea has carried out three nuclear tests in the last eight years, the most recent of which was in February 2013.



Each time the United Nations Security Council has reacted with increased sanctions.