US President Joe Biden last week asked his Chinese counterpart, Xi Jinping, if he could try to talk North Korea out of a new nuclear weapon test but he acknowledged that he did not know if China had the capacity to do so.
As unpredictable North Korea builds its arsenal of nuclear weapons and the missiles to fire them across Asia and at the United States, the question of China's ability to rein in its old ally has taken on particular urgency.
But with tension simmering between the United States and China, especially over Taiwan, the issue may not only be if China has the ability to influence North Korea's behaviour but to what extent it is in China's interests to tame a neighbour it has long seen as a useful buffer to the United States.
"From China's ... perspective, North Korea can serve as a force multiplier to challenge America’s position in the Pacific," said Craig Singleton, a former US government official now with the Foundation for Defense of Democracies.
"Simply put, the more countries willing to challenge or complicate the US-led security order in the Indo-Pacific, the better."
North Korea tested an intercontinental ballistic missile on Friday last week, just as leaders of the Asia-Pacific Economic Cooperation forum were gathering in Bangkok, the latest in a series of missile tests that has raised fears that the isolated country is about to test a nuclear weapon for the first time since 2017.
Even before Friday's missile launch, Biden raised the stakes when he told Xi at last week's G20 gathering in Indonesia that North Korea's development of weapons would lead to an enhanced US military presence in the region.
China does not want to see a nuclear-armed North Korea, nor does it want to see US nuclear weapons in the region, but the prospect of an expanding US military footprint raises other priorities for China, said Jenny Town of 38 North, a Washington-based North Korea project.
"They see the United States, South Korea and Japan forming as a security bloc, creating a need for a counter bloc, which would include North Korea," she said, referring to China.
"So any decision to be tough on North Korea has to be weighed against what they see as a growing incentive to deepen relations with security partners.”
'ROLE TO PLAY'
China fought beside the North in the 1950-53 Korean War and has backed it economically and diplomatically ever since but its influence over the resourceful regime is limited.
"Americans have perennially overestimated China's influence over North Korea," said John Delury, professor of Chinese studies at Yonsei University in Seoul.
North Korea has for years demonstrated a willingness to endure sanctions to develop the weapons it regards as vital to defend itself from a United States it believes is bent on regime change.
Even during years of self-imposed COVID isolation, North Korea kept up the work on its weapons.
"What is China going to do?" Delury asked. "Sanction North Korea, which cut itself off from the world for three years because of COVID and continued testing missiles? The whole point is China doesn’t control North Korea."
Nevertheless, a senior US administration official said the United States was in regular contact with China in the hope it can help persuade North Korea to stop alarming the region with displays of its nuclear ambitions.
"We do think that Beijing has a role to play," the US official said. "It will definitely be part of our diplomacy to try to get China to ... use its influence."
China's foreign ministry referred to North Korea's "reasonable concerns" and called for a "balanced solution" in accordance with what it calls a "two-track approach" of promoting denuclearisation and establishing a peace mechanism on the Korean peninsula.
"China has always been committed to maintaining peace and stability on the peninsula ... It is willing to work with all parties," it said this week in response to a question about its policy.
Tong Zhao, a visiting research scholar at Princeton University's School of Public and International Affairs, said if North Korean leader Kim Jong Un feels compelled to conduct a nuclear test to develop his prized deterrent he is unlikely to be put off.
"If North Korea has an inherent technical need to do the test, then I don't think China has real leverage to stop those activities. The most China may be able to do is to delay those tests," he said.
"I don't think China has leverage to fundamentally change Kim Jong Un’s decision-making."