US Secretary of State John Kerry has sharply criticised North Korea for carrying out a fourth nuclear test, despite international warnings.
Kerry has also been reiterating calls for more international sanctions to be implemented against Pyongyang.
North Korean state media announced that a successful test of a hydrogen bomb had taken place on 6 January. Experts are sceptical about the claim.
“(North Korean leader) Kim Jong Un’s actions are reckless and they are dangerous,” Kerry said at a joint news conference with Chinese Foreign Minister Wang Yi.
“Whether or not he achieved the explosion of a hydrogen weapon is not what makes the difference. It’s that he’s trying, that he wants to do that and made the attempt.”
North Korea is isolated from much of the rest of the world, and China is its main link with the international community.
Kerry called the latest North Korean test “a blatant violation of the UN Security Council Resolution”, adding that “as permanent members of the Security Council our two countries (US and China) and other countries are required to take action.”
The so-called six-party talks between North Korea and South Korea, the US, China, Russia and Japan have been stalled since December 2008.