North Korea is preparing for a third underground nuclear test, the South Korean news agency Yonhap reported on Sunday, referring to intelligence officials.
"North Korea is making clandestine preparations for a third nuclear test at Punggye-ri in North Hamkyong Province, where it conducted two nuclear tests in the past," the agency quoted an intelligence official as saying on condition of anonymity.
Satellite images show the reclusive communist regime digging a new tunnel underground in the Punggye-ri nuclear test site in the country's northeast, where it conducted two previous nuclear tests, first in 2006 and then in 2009.
The construction is believed to be in its final stage, the intelligence official told the agency.
North Korea, which withdrew from the six-party disarmament talks on its nuclear program three years ago, agreed in February to suspend uranium enrichment, as well as nuclear and long-range missile tests in return for U.S. food aid, opening the way for the restart of negotiations.
The move is seen as a violation of a UN Security Council resolution and has drawn international condemnation. The United States and other countries suspect that the launch is a thinly veiled ballistic missile test.