South Korean Foreign Minister Kim Sung-hwan telephoned U.S. Secretary of State John Kerry on Tuesday and they agreed to take "swift and unified" action at the U.N. Security Council over North Korea's third nuclear test, Seoul's foreign ministry said Tuesday.

North Korea's state media confirmed that it has successfully carried out a third nuclear test, using a miniaturized device that yielded a greater explosive force than previous tests. South Korea condemned the test as a violation of U.N. Security Council resolutions.

"Minister Kim and U.S. Secretary of State Kerry held a emergency consultation by telephone and agreed to take a swift and unified action at the U.N. Security Council," foreign ministry spokesman Cho Tai-young said.

The U.N. Security Council will hold an emergency meeting at 9:00 a.m. on Tuesday (New York time), Cho said.

South Korea has also been in "close consultations" with China, the spokesman said.

Lim Sung-nam, Seoul's chief nuclear envoy, has telephoned his U.S. and Japanese counterparts and discussed measures in response to the North's nuclear test, Cho said.

Seoul officials said the North's nuclear test was conducted at 11:57 a.m. on Tuesday, with the defense ministry estimating the yield at 6 to 7 kilotons. (Yonhap News)