WASHINGTON (AP) — China's surprising suspension of North Korean coal imports puts pressure not only on Pyongyang, but also on President Donald Trump. The question for him: Should the U.S. respond with new North Korea negotiations?

Years of failed efforts to stem North Korea's nuclear and missile programs have followed a usual pattern. The United States seeks tougher action from China, the North's traditional ally. Beijing urges U.S. diplomatic engagement.

But China's move this weekend appears to change the dynamic, addressing the long-standing American demand, one Trump has vociferously repeated. If enforced, the loss of coal revenue could tighten the screws on leader Kim Jong Un after his government's acceleration of nuclear and missile tests this last year.

China rarely makes concessions for free, and will want Trump to respond in kind.

"If China is squeezing North Korea, it is for one purpose and one purpose only: to offer a cooperative gesture to the incoming Trump administration in return for an initiative on negotiations," said Stephan Haggard, a North Korea expert at the University of California, San Diego.

Beijing indicated such a strategy was in play.

Foreign Ministry spokesman Geng Shuang said the country wants parallel negotiations on nuclear matters and a formal peace treaty to replace the armistice ending the 1950-53 Korean War — a longstanding North Korean request. Washington has said the North's nuclear weapons program must be settled first.

Meanwhile, the newspaper of China's ruling Communist Party, Global Times, published a pair of editorials Wednesday calling for aid-for-disarmament talks to restart. They've been on ice since 2009.

Any breakthrough would almost surely require U.S.-Chinese cooperation. Kim has shown little interest in relinquishing his nation's nuclear deterrent as he closes in on a weapon capable of targeting mainland America, and Sino-American disputes over the best approach to dealing with the confounding North Korean leader have hamstrung international diplomatic efforts.

"We continue to urge China to exert its unique leverage as North Korea's largest trading partner to convince Pyongyang to return to serious talks on denuclearization," State Department spokeswoman Anna Richey-Allen said.

Trump has vowed to "deal with" North Korea, without saying how. His administration is conducting a broad-ranging policy review, including how to make sanctions bite. Negotiations haven't been ruled out, said a U.S. official, who wasn't authorized to discuss internal deliberations and demanded anonymity.

China's decision on coal could change the U.S. calculus. A second administration official described it as a potentially hopeful sign, though the U.S. was still gauging the significance.

North Korea's coal exports to China totaled $1.2 billion last year, according to Chinese customs, representing more than a third of the North's total export income.

Geng, the Chinese spokesman, explained China's decision by saying the coal imports this year already "approximated" a $400 million annual cap set by the U.N. Security Council.

But China has exploited loopholes in the past, raising questions about alternative motivations. These could include embarrassment over the apparent assassination of Kim Jong Nam, the North Korean leader's exiled, half-brother who was spending much of his time in China. Or, a pre-emptive effort to forestall a new U.S.-South Korean missile defense system.

Regardless of motive, "enforcement will be the key," said Joseph DeThomas, a former U.S. diplomat who advised the Obama administration on sanctions. DeThomas, now a professor at Pennsylvania State University, said China's suspension could cost Pyongyang hundreds of millions of dollars in much-needed hard currency.

But Troy Stangarone, senior director at the Washington-based Korea Economic Institute, questioned how significant the economic impact would be. Official Chinese figures don't account for services and illicit border trade between the countries, he said.

China has long resisted applying severe economic pressure on North Korea. While it opposes the North's pursuit of nuclear weapons, Beijing fears any policies that might lead to an influx of North Koreans into China or a U.S.-allied, unified Korea emerging on the Chinese border.

In any case, questions will now be asked of the Trump administration.

As a presidential candidate, Trump expressed a willingness to speak with Kim — a politically risky move given North Korea's history of reneging on past agreements. President Barack Obama refused to re-engage without a commitment from the North to pursue denuclearization, cranking up sanctions while waiting. The approach failed to stop Pyongyang's rapid advances in weapons development.

Trump will need to come up with a strategy soon. A high-profile North Korean defector reported that Kim wants to finish an intercontinental ballistic missile capable of hitting the U.S. mainland in the next year.

It's unclear what, if anything, Trump can offer Kim to bargain over a nuclear program he likely sees as essential to the survival of his totalitarian regime.

Stangarone said the question for Kim becomes this: "Can he weather whatever storm is coming and finish the program and make this fait accompli?"

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EDITOR'S NOTE — Matthew Pennington has covered Asian affairs for The Associated Press since 1999.

Associated Press writer Christopher Bodeen in Beijing contributed to this report.