Li will be the highest level Chinese official to visit North Korea since Xi came to power in 2012. The last Politburo Standing Committee member to go to Pyongyang was Liu Yunshan, in 2015.

US President Donald Trump said in late August that he did not believe Beijing was “helping with the process of denuclearisation as they once were” – a remark China’s foreign ministry described as contrary to the facts.

Li’s visit comes as progress has stalled between Washington and Pyongyang following the landmark summit between Trump and North Korean leader Kim Jong-un in Singapore in June.

Also late last month, Trump cancelled a planned trip to the North by Secretary of State Mike Pompeo.

That was followed by US Defence Secretary James Mattis saying America did not plan to suspend more joint military drills with South Korean forces amid reports Pyongyang was rejecting US demands to give up its nuclear warheads.

China slams ‘absurd logic’ from US after Trump accuses Beijing of blocking North Korea denuclearisation

Relations between China and North Korea had deteriorated over Pyongyang’s nuclear and missile tests that prompted Beijing to back United Nations sanctions against the regime.

But ties have thawed this year, with North Korean leader Kim Jong-un visiting China three times since March. Observers suggested the first two visits were an effort by Kim to boost his bargaining power with Trump ahead of their summit, and to push for economic cooperation with China.

“With Trump stepping up his rhetoric against China over trade and North Korea, Xi going to Pyongyang would probably reinforce his thinking that Beijing has not been enthusiastic enough about denuclearisation,” said Zhang Baohui, an international relations professor at Lingnan University in Hong Kong.

“Sending Li as a top official representative will help as a goodwill gesture to North Korea, but it avoids reinforcing Trump’s thinking.”

Boo Seung-chan, a research fellow at the Yonsei Institute for North Korean Studies in Seoul, said Xi appeared to have made a strategic decision to protect China’s national interests by trying to improve its relations with the US.

Ju Kyu Chang, developer of North Korea missiles and nuclear weapons, dies at 89

“If Xi went to Pyongyang after Trump’s warning, it could worsen the US tariffs situation for China and this ‘assertive China’ view held by other nations,” Boo said, adding that more trade actions would also make it difficult for China to pursue its goals.

“However, this does not mean relations between China and North Korea will worsen. Xi has carefully chosen his right-hand man, who he trusts to go in his place, which will show Pyongyang that it’s still important to Beijing,” Boo said.

Watch: North Korean defectors speak out against atrocities

“China’s strategy has not changed and so its relations and policies towards the North are also unlikely to change.”

The anniversary on September 9 is one of the hermit kingdom’s most important annual holidays, along with the birthdays of late leaders Kim Il-sung and Kim Jong-il.

Lu Chao, a Korean affairs expert at the Liaoning Academy of Social Sciences, said sending Li to the anniversary celebrations was a sign China wanted to keep the momentum going in its relations with North Korea, even though Xi did not appear to be attending the event.

“It means that China still holds its relations between the state and party of North Korea in high regard, and it’s a sign of China’s support for North Korea’s strategy,” he said.

Lu added that Pyongyang was likely to seek Beijing’s help in getting international sanctions against North Korea lifted, but that China would be pushing for its isolated communist neighbour to take more steps towards denuclearisation.

Michael Kovrig, senior adviser for Northeast Asia at the International Crisis Group, said Li would have the political savvy and foreign policy experience to gather insights about Pyongyang’s intended approach to negotiations with the US and South Korea.

He added that sending Li to the event showed that North Korea’s standing had improved in China’s eyes.

Additional reporting by Lee Jeong-ho