Beijing (AFP) - When China called on the United States to engage in direct talks with North Korea, it probably never imagined it would be absent from the table.
Beijing, which chaired failed international talks on North Korea that collapsed a decade ago, has long seen itself as central to the negotiations to end Pyongyang's nuclear programme.
But when US President Donald Trump agreed last week to hold a historic meeting with North Korean leader Kim Jong Un at a yet-to-be-decided day and place, China was nowhere to be seen.
Chinese President Xi Jinping has not even met Kim since the young North Korean autocrat took power following his father's death in 2011.
While China remains North Korea's only ally and main economic lifeline, relations between the two neighbours have soured as Xi, under pressure from Trump, has backed a slew of UN sanctions to punish Pyongyang for its nuclear and missile tests.
In a Friday phone call with Trump, Xi praised the US leader's "positive" move, saying he hoped the US and North Korea would start talking as soon as possible and that China was devoted to solving the nuclear issue through dialogue.
But not everyone was so happy: China's top-selling nationalist tabloid the Global Times dashed out an editorial aimed at soothing the jangled nerves of Chinese patriots afraid that the country would be sidelined by a Trump-Kim love-in.
"Chinese people should stay calm and remain poised, and avoid the mentality that China is being marginalised," it said.
"China's prime interest on the Korean peninsula is its denuclearisation and peace, both of which are more important than China's relations with North and South Korea and power politics."
- Nuclear fears -
Trump's surprise agreement to meet Kim appears to have shocked many in China, who wonder if the Asian giant -- which is increasingly trying to put itself at the centre of global diplomacy -- has been cut out of the loop by Pyongyang.
"Given that parts of Trump's own national security team were not informed of this major change in policy, I'm doubtful that President Trump informed the Chinese, and definitely not with any significant lead time," said Oriana Skylar Mastro, an expert on China, North Korea relations at Georgetown University and the American Enterprise Institute.
While Washington is happy to use China to squeeze North Korea economically, it is not as interested in involving Beijing in the more delicate work of negotiations.
"The Trump administration sees China as primarily an obstacle to the peaceful resolution of the DPRK nuclear issue and not so much as a critical diplomatic interlocutor," Skylar Mastro said.
But Seoul, which has sought to improve its strained ties with Beijing, sent its national security adviser Chung Eui-yong to brief Xi on the recent breakthrough on Monday and thank him for his help.
Xi's leadership has played "a big role" in these "positive changes", Chung told the Chinese president, adding that Seoul expects China to continue to play an "active and leading role".
It is natural that Beijing would have reservations about what a Kim-Trump meeting could mean for its own interests in the region, said Zhang Liangui, a professor of the International Strategic Academy of the Party School of the Central Committee of the Communist Party.
"As a neighbour, if North Korea continues to develop nuclear weapons, China could be the biggest casualty," he told AFP. "So you could say, China is the most important party involved."
Those concerns came sharply into focus when North Korea literally shook China with an underground nuclear test that produced an earthquake felt over the border.
Beijing also worries that Kim's weapons could trigger an arms race in the region, leading its historical rival Japan and perhaps even South Korea to seek nuclear weapons.
- Six parties -
While China has long pushed for US-North Korean dialogue, it always saw it as a first step towards returning to the long-dormant Six-Party Talks, which grouped China, the US, Japan, Russia and the two Koreas.
North Korea abruptly quit the forum in 2009.
"Beijing would be most comfortable to play the mediating role," said Wenran Jiang, senior fellow at the Institute of Asian Research of the University of British Columbia.
China "still believes" that all six parties must be part of the denuclearisation process, he said.
Xi and his "very experienced foreign policy team seem to have displayed a high level of confidence that China is too big and too important to be left out of the negotiations."
"They are waiting patiently for the right opportunity and they are quite certain relevant parties will knock on China's door soon."
Bonnie Glaser, senior adviser for Asia at Washington's Center for Strategic and International Studies, said China may offer to host the Trump-Kim meeting, which would "at least increase the possibility that they will be heard."
"The Chinese traditionally have always worried about the US and North Korea cutting a deal at their expense," she said, adding that "people in the US have always laughed at those concerns."