South Korea has detected signs that the North is preparing for a fifth nuclear test, President Park Geun-hye said.
She did not elaborate on what the signs where, but ordered the military to be prepared, Yonhap news agency said.
It comes after reports in local media about increased activity at the North’s Punggye-ri nuclear test site, where the previous nuclear tests took place.
A new test would be further defiance of tougher sanctions imposed by the UN last month.
“We are in a situation, in which we don’t know whether North Korea could stage provocation as a move to overcome its isolation and to consolidate its internal unity,” Ms Park said told her top aides, Yonhap reported.