North Korean leader Kim Jong Un briefed Chinese President Xi Jinping on Tuesday about his historic summit with US President Donald Trump, a visit that underscores Beijing's efforts to remain at the centre of fast-moving nuclear diplomacy.

Xi urged the US and North Korea to implement the agreements reached at the June 12 summit in Singapore, while Kim thanked Xi for his role in the diplomatic efforts, according to Chinese state media.

Kim's third trip to China since March comes as Beijing tries to strengthen its role as a mediator between the US and the North, where it claims compelling security and economic interests.

The North's leader, who is believed to have landed in the Chinese capital on Tuesday morning, was greeted with a military honour guard at the ornate Great Hall of the People, as the Cold War-era allies repair ties that worsened when Pyongyang tested nuclear weapons and Beijing backed UN sanctions.

Kim “felt thanks for and highly praised China's promotion of denuclearisation of the Korean Peninsula and its important role in protecting the peninsula's peace and stability,” state broadcaster CCTV said.

North Korea “hopes to work with China and other concerned parties to promote and establish a solid, long-lasting peace mechanism on the Korean Peninsula and make joint efforts to achieve a lasting peace on the peninsula.” For his part, Xi told Kim he “wants North Korea and the US to carry out the results of their leadership summit”, the report said.

Trump and Kim pledged in a joint summit statement to “work toward the complete denuclearisation of the Korean Peninsula”.

In return, Trump made the shock announcement that he would stop joint military drills with South Korea, long seen as a provocation by Pyongyang and Beijing. The US and South Korean militaries confirmed on Tuesday they have called off a major joint exercise.

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Kim told Xi his summit with Trump “achieved results that are in line with the interests of all parties and the expectations of the international communities,” according to CCTV.

“If the two parties can solidly implement the summit's consensus step by step, it will open a new, important phase of the denuclearisation of the Korean Peninsula.”

The United States relies on China to enforce UN economic sanctions against the North, giving Beijing potential leverage in its looming trade war with Washington.

“I think that North Korea can be another card Beijing can play to win leverage in negotiations with Washington,” Yang Moo-jin, professor at Seoul's University of North Korean Studies, told AFP.

Following the Singapore summit, China suggested the UN Security Council could consider easing the economic restrictions.

Wang Dong, an international relations expert at Peking University, said he expected Kim to ask China for help in easing the sanctions in return for his pledge to denuclearise.

“The Chinese and North Korean leaders are carrying out consultations on how to jointly move the Korean nuclear issue forward,” Wang said.

China may not have been at the table in Singapore but it retains strong influence behind the scenes, Wang said.

Tuesday's visit shows that “China is indispensable to the entire Korean nuclear issue,” he said.

'Differences ahead'

Trump had hailed Kim's denuclearisation pledge as a concession. But critics said the stock phrase long used by Pyongyang stopped short of longstanding US demands for North Korea to give up its atomic arsenal in a “verifiable” and “irreversible” way.

It was urgent for Xi and Kim to discuss how North Korea would work towards meeting US demands, said Beijing-based international relations commentator Hua Po.

“There may be differences ahead between the DPRK (North Korea) and the US in regards to denuclearisation, because the US wants irreversible and verifiable denuclearisation. It may be difficult for Kim Jong Un to accept,” Hua told AFP.

“Therefore, both China and the DPRK want to strengthen communication and form an overall strategy to deal with the United States going forward,” Hua added.

Analysts saw the summit outcome as a sign of China's influence.

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Beijing has repeatedly called for a “suspension for suspension” approach, under which the North would stop its nuclear and missile tests in exchange for the US and South Korea halting military exercises.

Washington had previously rebuffed the proposal.

Kim will be in Beijing through Wednesday, state media reported.

His two previous trips to China, including his maiden official voyage abroad in March, had been kept secret until he returned home.

“I think that China convinced North Korea that high-profile trips like this can no longer be kept secret for so long,” said Yang, the Seoul analyst.

“Also Kim Jong Un is seeking to establish this image as a normal leader of a normal country in the international community. “