South Korea's Defense Ministry warned Monday that North Korea could conduct another nuclear test at any time.
Spokesman Moon Sang-gyun declined to give more information beyond saying a potential test could take place in an unused tunnel at the Punggy-ri site where North Korean has previously carried out tests in its effort to develop nuclear warheads that can fit on a missile.
The latest test happened Friday. It was the fifth that North Korea has done and the most powerful to date.
The U.N. Security Council denounced the test, saying it was a flagrant violation of sanctions imposed during the past decade in response to North Korea's nuclear activity. A council statement pledged to work on "appropriate measures" in response.
At a U.S.-South Korea defense meeting Monday in Seoul, South Korean Deputy Defense Minister for Policy Yoo Jeh-seung said the biggest threat to the alliance between those two nations is North Korean leader Kim Jong Un who considers nuclear weapons "tools of survival for the regime."
The U.S. and South Korea joined with China, Russia, Japan and North Korea in six-party talks aimed at curbing the North Korean nuclear weapons program in exchange for aid, but those negotiations broke down in 2009.