Image copyright AP Image caption John Kerry (L) met Xi Jinping and Foreign Minister Wang Yi (R)

US Secretary of State John Kerry says Chinese officials have reassured him that they will work to rein in North Korea's nuclear programme.

After meeting President Xi Jinping and Prime Minister Li Keqiang, Mr Kerry said he was satisfied that China "would not allow a nuclear programme over the long run" in North Korea.

China is North Korea's main ally and trading partner.

Mr Kerry will visit Jakarta next as part of a "pivot to Asia" tour.

He described the meeting in Beijing as "very constructive".

He said China "will not allow instability and war to break out in the region", and said Beijing was prepared to take "additional steps" if Pyongyang did not comply.

Mr Kerry refused to be drawn on what specific measures China would take.

China has already been steadily turning up the pressure on North Korea to forgo nuclear weapons.

In September last year, China banned the export of several weapons technologies to North Korea that could have been used to develop nuclear weapons.

China has also supported several UN Security Council resolutions imposing sanctions against North Korea over the nuclear issue.

Mr Kerry said earlier on his Asian tour that the US wanted Pyongyang to return to stalled six-nation talks aimed at ending its nuclear programme.

'National Interests'

Mr Kerry said his talks Beijing also tackled China's territorial disputes with its South-East Asian neighbours.

He said he warned China against any moves to declare an air-defence zone in the South China Sea.

Last year Beijing set up an air-defence zone in the East China Sea, around islands that it disputes with Japan.

The US said at the time that it "neither recognises nor accepts" the zone.

However, the BBC's Michael Bristow says China does not seem to be listening to Mr Kerry's advice on its territorial disputes.

Foreign Minister Wang Yi said his country was determined to protect its national interests.

Mr Kerry's regional tour began in South Korea on Thursday, and he is due to visit Jakarta next.