WASHINGTON: US President-elect Donald Trump indicated a tougher US approach to China by speaking to Taiwan's president last week, but how far he will push a risky test of wills to wring concessions from Beijing on issues from trade to North Korea is unclear.

The call between Trump and Tsai Ing-wen was the first by a US president-elect or president with a Taiwanese leader since President Jimmy Carter switched diplomatic recognition to China from Taiwan in 1979.

It prompted a diplomatic protest from China which the outgoing Obama administration warned could undermine progress in relations with Beijing, which has been carefully built up over decades by both Republican and Democratic administrations.

Analysts say it could provoke military confrontation with China if pressed too far.

Trump officials and Vice President-elect Mike Pence sought to play down the significance of the 10-minute conversation, saying it was a "courtesy" call and not intended to show a policy shift.

However, Trump fueled the fire on Sunday by complaining about Chinese economic and military policy on Twitter, while on Monday an economic adviser to Trump, Stephen Moore, said if Beijing did not like it, "screw 'em."

Analysts, including senior former US officials, said the call appeared to be at least an initial shot across China's bow to signal a tougher approach to Beijing, which includes plans for a buildup in the US military, in part in response to China's growing power in the Asia-Pacific region.

Jon Huntsman, reportedly among the candidates to become Trump's secretary of state, was quoted by The New York Times as saying at the weekend that Taiwan might prove a "useful leverage point" in dealings with China.

Trump adviser and China hawk Peter Navarro, and former US Ambassador to the United Nations John Bolton, another in the mix for the top US diplomatic role, have both proposed using degrees of escalation on Taiwan to pressure China to step back from its pursuit of territory in East Asia.

Navarro, who has produced books and multipart television documentaries warning of the dangers of China's rise, has suggested stepped up engagement with Taiwan, including assistance with a submarine development program.

He argued that Washington should stop referring to a "one-China" policy, but stopped short of suggesting it should recognize Taipei, saying “there is no need to unnecessarily poke the Panda.”

Bolton though, in an article in January, countenanced a "diplomatic ladder of escalation" that could start with receiving Taiwanese diplomats officially at the State Department and lead to restoring full diplomatic recognition.

Evan Medeiros, a former official who served as President Barack Obama's top adviser on East Asia, said this was a highly risky strategy.

"Here’s the reality: China let us all know very clearly in the mid-1990s that the Taiwan issue is a war-and-peace issue," Medeiros said. "Is that a proposition that the US should test?

"The Taiwan issue is so politically sensitive and ranks so high in Chinese priorities of interest they are not going to begin trading anything away for it. And if the US decided to establish formal diplomatic relations with Taiwan, it could easily precipitate a military crisis in Northeast Asia," he said.

Douglas Paal, a White House official under Republican administrations who served as US representative to Taiwan from 2002-2006, said the approach of Trump advisers seemed rooted in the 1990s, when China was much weaker and the United States in a better position to take a tougher line.

"The problem is that Beijing decided in 1996 on a 10-year (military) buildup so that it would never have to swallow such stuff again," Paal said.

TEST OF WILLS

He said Chinese President Xi Jinping is seeking to cement his position at a congress of the ruling Communist Party next year.

"Were he to look soft on something like making the US office in Taipei into an official diplomatic outpost, Xi would be devoured by his rivals, and he won’t let that happen," Paal said.

Chris Murphy, a Democratic member of the US Senate Foreign Relations Committee, said using Taiwan as a way to pressure China to cooperate on North Korea's nuclear program or on trade could be counterproductive.

"Pressing China on Taiwan won't likely bring them to the table on North Korea and currency," he wrote on Twitter. "Risks backing them into a dark, nasty corner."

Two sources familiar with the debate on China policy within the Trump camp said Bolton and other hard-liners had encouraged Taiwanese leaders to approach the president-elect.

However, former US Secretary of State Henry Kissinger and others advising Trump and his transition team have cautioned against an open break with the four-decade "One China" Policy, they said.

As a result, Trump first presented the request for a phone conversation as a personal matter rather than a harbinger of a shift in US policy, which left Japan and other US Asian allies unfazed.

However, the sources said that after Trump tweeted about Chinese currency manipulation, import tariffs and the South China Sea, some Asian leaders were asking whether he was deliberately provoking China, potentially leading to a dangerous escalation of tensions.

Chas Freeman, a former US diplomat who was then-President Richard Nixon’s interpreter on his historic trip to China in 1972, said he thought Chinese officials were waiting to see what Trump's intentions were as president.

"They (Chinese) don’t want to humiliate Mr. Trump or get into an emotional confrontation with him," he said.

"So the immediate impact of this will be they will give him the benefit of the doubt, that he didn’t know what he was doing, and didn’t understand the significance of this, that perhaps he was manipulated by people around him."