The US and Chinese presidents face an awkward encounter at the G20 summit this week as rising tensions over how to deal with North Korea threaten to shatter the already-crumbling facade of their friendly rhetoric.

North Korea's landmark test of an intercontinental ballistic missile (ICBM) capable of reaching Alaska has intensified friction between the superpowers ahead of US President Donald Trump's meeting with his Chinese counterpart Xi Jinping at the summit in Germany, which starts Friday.

In the weeks leading up to Tuesday's missile test, Trump had used a series of Twitter outbursts to criticise China over its failure to rein in the nuclear-armed North, vexing Chinese leaders who prefer closed-door diplomacy to public tongue-lashings.

In a marked change of tune, Trump has gone from calling Xi a "good man" after their first face-to-face meeting at the US billionaire's Florida resort in April to accusing him last month of failing to resolve the North Korea issue.

In his latest salvo on Monday, Trump called on China to "put a heavy move on North Korea and end this nonsense once and for all!"

China's foreign ministry responded that Beijing had made "relentless efforts" to resolve the issue.

For his part, Xi complained in a call with Trump on Monday about a "negative" patch in relations after the US administration slapped sanctions on a Chinese bank linked to North Korea and authorised a $1.3 billion arms sales to Taiwan.

While China, the North's sole major ally and economic lifeline, could do much more to starve Pyongyang of the foreign currency it needs to fund its weapons programmes, analysts say the US actions make that less likely to happen.

- 'Delicate balance' -

China is also carefully calibrating its moves to avoid destabilising its unpredictable neighbour for fear of triggering the regime's collapse and a flood of refugees across its border -- or giving the US a reason to launch a strike in its backyard.

"They are trying to find the point to keep the Americans happy and keep Trump from veering off and looking at military options," said Andrew Gilholm, director of analysis of Greater China and North Asia at Control Risks.

Gilholm added, however, that China's economic leverage over the North did not necessarily mean it could persuade Pyongyang to give up its nuclear ambitions.

But the North's possession of a working ICBM could signal time is running out for China to act.

Trump, who has made halting the nuclear threat his top foreign policy priority, has vowed to act unilaterally against Pyongyang if Beijing fails to rein in North Korean leader Kim Jong-Un's regime.

"It's a delicate balance," said Willy Lam, a politics expert at the Chinese University of Hong Kong.

"If they (China) don't take action fast enough it's possible that the US might contemplate some action, either a surgical strike or other action."

China appeared to cave to US pressure in February when it announced the suspension of coal imports from North Korea for the rest of the year.

The total value of all imports from North Korea fell to $721.5 million between January and May from $773.6 million over the same period last year, according to Chinese official figures.

- 'Impasse' -

While the US has traditionally favoured sanctions as a pressure tactic against the North, China has been pushing for the resumption of six-party negotiations that have been dormant since 2009.

Xi, on a visit to Moscow on Tuesday, got Russian President Vladimir Putin to back his "dual track" proposal for North Korea to freeze its nuclear activities in return for the US and South Korea to halt joint military drills.

But analysts said China could try to appease the United States by doing more to crack down on Chinese banks, companies and airports with ties to the North or even reducing food and fuel supplies to the hermit state.

"What makes the difference is not whether the UN takes any measures, it's how far China goes in implementing them," said Gilholm, referring to UN sanctions on North Korea.

Xi might be inclined to act if it means avoiding an embarrassing crisis ahead of a key Communist Party congress later this year, which is due to cement his position as the most powerful Chinese leader in a generation.

But Lam said Xi would likely take covert action so he is not "seen as failing to stand up to the Americans" after the Trump administration took steps last week that angered China.

As the two leaders prepare to meet at the G20 a breakthrough on North Korea is looking unlikely, said Michael Cole, a Taipei-based academic with the University of Nottingham's China Policy Institute.

"We're at an impasse," Cole said.

source: AFP