Since the US presidential campaign, Donald Trump’s fiery and antagonistic attacks on China regarding issues ranging from currency and trade to Taiwan and the South China Sea have prompted much speculation that the world’s two largest economies are embarking on a dangerous path of confrontation.

But the first test of the bilateral relationship was passed relatively soon into the presidency, when Trump told President Xi Jinping ( 習近平 ) in a phone call this month that he would honour the one-China policy, an about-turn from his previous remarks that he intended to use Taiwan as a bargaining chip to gain concessions from China.

Now, with ties returning to a slightly warmer basis and both sides trying to figure out how to steer the relationship forward, North Korea has provided a good opportunity for Beijing and Washington to assess the possibilities for greater cooperation.

On February 18, China’s Ministry of Commerce suddenly announced a ban on imports from North Korea, effective from the following day until the end of the year. The surprise move is significant on multiple levels. The ban sends an unusually strong message to Pyongyang, as coal is its largest export item and China accounts for more than 90 per cent of North Korea’s foreign trade.

It also sends a message to Trump, who has complained loudly that Beijing is not doing enough to contain North Korea’s nuclear proliferation.

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Chinese officials said only that the ban was an implementation of the latest United Nations Security Council resolution that tightened sanctions against the regime in the wake of its last nuclear test.

Yet timing is everything in diplomacy, and the timing of the announcement of the ban suggests much closer communication between Beijing and Washington than is acknowledged publicly.

Given its urgency and importance, the North Korean issue may have been a large part of the telephone conversation between Xi and Trump. Trump has described the conversation as “a long talk” in which “a lot of subjects” were discussed.

Over the past week or so, China’s top two foreign affairs officials – Foreign Minister Wang Yi ( 王毅 ) and State Councillor for Foreign Affairs Yang Jiechi ( 楊潔箎 ) – have spoken with or met US Secretary of State Rex Tillerson and it’s likely that North Korea was high on their agenda.

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During a phone call last Tuesday, Tillerson and Yang “agreed on the need to address the threat that North Korea poses to regional stability”, according to a statement from the US State Department.

A Xinhua report said “the two sides exchanged some views on a number of international issues”, though it did not mention a specific topic.

However, it did quote Yang as telling Tillerson that Beijing and Washington should strengthen pragmatic cooperation to further bilateral relations.

Well, how to contain North Korea and remove its nuclear threat can and should be one of the major issues the two sides work on during Trump’s presidency. Doing so is in the interest of both countries and, indeed, the world. China’s reluctance to do anything that might threaten the stability of the North Korean regime is not only because it fears a collapse would trigger a flood of refugees into its northeastern provinces but because in a reunified Korea US troops currently based in the South could be moved right up to the Chinese border.

But Beijing’s patience with its neighbour has been running thin, particularly since Xi and Kim Jong-un came to power. Xi and other Chinese leaders are widely believed to have been angered by Kim’s erratic behaviour and North Korea’s nuclear test last year. That test, at a site so close to the Chinese border, has also stirred very strong feelings among the mainland public.

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Over the past week, the mounting evidence that Pyongyang was behind the assassination of Kim Jong-nam, Kim Jong-un’s half brother, in Malaysia, has further angered China, which had been protecting Jong-nam since he was exiled years ago.

Moreover, the diplomatic tussle resulting from the assassination will seriously sour economic and trade relations between Korea and Malaysia and other Southeast Asian countries including Indonesia and Vietnam – the other major sources of trade for North Korea, other than China. Malaysia has reciprocal visa-free arrangements with North Korea. In this context, China’s ban on coal imports will be particularly biting if it is maintained.

But for Beijing to continue to turn the screw on North Korea, Washington will have to address Chinese concerns such as the US decision to deploy the THAAD anti-missile system in South Korea, which Beijing views as threatening its own security interests.

Trump’s assertion that Beijing should bear sole responsibility for containing North Korea is simply wrong. Beijing’s efforts to push for the six-party talks, which also involve South Korea, Japan, and Russia, have largely failed, partly because North Korea has always sought direct dialogue with Washington.

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Now the ball is in Trump’s court. Analysts have long called for fresh thinking on how to contain North Korea, so Trump’s reputation for being unconventional might be just what’s needed.

Using North Korea as a bargaining chip, if it is done in the right way, may well bring the kind of pragmatic cooperation between Washington and Beijing that State Councillor Yang has advocated.

Wang Xiangwei is the former editor-in-chief of the South China Morning Post. He is now based in Beijing as editorial adviser to the paper