North Korea's "words and actions continue to be very hostile and dangerous to the United States," US President Donald Trump said on Twitter, in his first reaction after Pyongyang conducted its sixth and most powerful nuclear test on Sunday.
"North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success," Trump said in a second tweet.
"South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!" he added.
North Korea earlier said the hydrogen bomb test ordered by leader Kim Jong Un was a "perfect success" and was a "meaningful" step in completing the country's nuclear weapons program.
The announcement came hours after a large earthquake that appeared to be man-made was detected near the North's known nuclear test site.
(Writing by Robin Pomeroy; Editing by Susan Fenton)