US Secretary of State John Kerry, who is in Beijing for talks, called North Korea's nuclear ambitions a "threat to the world" and urged new sanctions.

But his counterpart Wang Yi suggested China would not support any sanctions.

China is North Korea's main ally, but has condemned Pyongyang's nuclear test.

On 6 January, a 5.1 magnitude tremor was detected in North Korea - which said it had successfully conducted an underground hydrogen bomb test.

However, nuclear experts questioned North Korea's claim, saying the size of the blast was not large enough to have been from an H-bomb.

 

Speaking on Wednesday after talks with Wang Yi, Mr Kerry said that both sides agreed on the need for a "strong" resolution against North Korea, and said that limiting the trade of goods and services across China's border with North Korea was one potential measure.

However, Mr Wang said that while China supported the need for a new resolution, it "should not provoke new tension in the situation, still less destabilise the Korean peninsula".

"Sanctions are not an end in themselves," he added.

China is Pyongyang's biggest trading partner, and major ally - although relations have cooled since Kim Jong-un succeeded his father.

Nonetheless, experts say China is wary of destabilising North Korea, fearing that millions of North Korean refugees could pour across China's borders if the regime collapsed.

 

The two sides also discussed the disputed South China Sea, where China has multiple competing territorial claims with other countries.

China has angered several neighbours by constructing artificial islands on claimed reefs, and building runways and other facilities on them.

Mr Kerry called on China to stop construction and land reclamation in disputed areas.

However, Beijing said such activity was within its legal rights to protect its territorial sovereignty.

Mr Kerry, who will also meet China's State Councillor Yang Jiechi and President Xi Jinping, is on an Asia tour that has included Laos and Cambodia.

Call for unity

In Laos and Cambodia, Mr Kerry had called on the two countries, who are members of the Association of Southeast Asian Nations (Asean), to present a united front against China on the South China Sea disputes.

Mr Kerry said Laos supported a "unified Asean" that would protect maritime rights.

However, Cambodia says any territorial disputes should be resolved bilaterally with China - a position supported by Beijing.

Laos is chairing Asean this year and, like Cambodia, shares a close economic relationship with China.