The top security officials of South Korea and the U.S. spoke on the phone to discuss responses to North Korea’s sixth nuclear test on Sunday.

The presidential office said that South Korea's National Security Office chief, Chung Eui-yong and his U.S. counterpart, Herbert McMaster held telephone talks for about 20 minutes from 1:45 p.m. Sunday, shortly after the North’s nuclear test.

President Moon Jae-in convened an urgent National Security Council(NSC) meeting at 1:30 p.m. to assess information and discuss response to the test.

Pyongyang issued a statement on Sunday afternoon and claimed it has successfully conducted a test of a hydrogen bomb mountable on an intercontinental ballistic missile.

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