广播听力: U.S. committed to defending South Korea, Japan: Clinton

"I want to underscore the commitments that the United States has and intends always to honour for the defence of South Korea and Japan. That is part of our alliance obligation which we take very seriously."

Clinton says North Korea is behaving in a "provocative and belligerent" manner toward its neighbours.

She urges Pyongyang to return to the six-party talks on abandoning its nuclear programs.

North Korea announced earlier this week it "successfully conducted one more underground nuclear test."

The country staged its first nuclear test back in 2006.