On Monday, White House spokesman Josh Earnest said progress with the Chinese could be "undermined" by a flare-up over the sovereignty of Taiwan, the self-governing island the U.S. broke diplomatic ties with in 1979. That split was part of an agreement with China, which claims the island as its own territory, although the U.S. continues to sell Taiwan billions in military equipment and has other economic ties.

Trump broke protocol last week by speaking with Taiwanese President Tsai Ing-wen, then took to Twitter to challenge China's trade and military policies.

"It's unclear exactly what the strategic effort is," Earnest said. "I'll leave that to them to explain."

So far, Trump's advisers have struggled to explain his action, sending mixed messages about whether the conversation with Taiwan's leader was a step toward a new policy or simply a congratulatory call. Incoming White House chief of staff Reince Priebus said Trump "knew exactly what was happening" when he spoke with Tsai, but Vice President-elect Mike Pence described the interaction as "nothing more than taking a courtesy call of congratulations."

Trump has pledged to be more "unpredictable" on the world stage, billing the approach as a much-needed change from President Barack Obama's deliberative data-style and public forecasting about U.S. policy. But Trump's unpredictability is likely to unnerve both allies and adversaries, leaving glaring questions about whether the foreign policy novice is carrying out planned strategies or acting on impulse.

China's authoritarian government likes predictability in its dealings with other nations, particularly the United States. The U.S. and China are the world's two largest economies with bilateral trade in goods and services reaching nearly $660 billion last year.

While there have been sharp differences between Beijing and Washington on China's island building in the South China Sea and over alleged Chinese cyber theft of U.S. commercial secrets, the two powers have cooperated effectively on climate change and the Iran nuclear deal.

Taiwan split from the Chinese mainland in 1949. American policy acknowledges the Chinese view that it has sovereignty over Taiwan, yet the U.S. considers Taiwan's status as unsettled. The U.S. is Taiwan's main source of weapons, with $14 billion in approved arms sales since 2009.

U.S. diplomats were shocked by Trump's telephone call with the Taiwanese leader. Several officials privately expressed deep unease that Trump's team did not inform the administration in advance or give it a chance to provide input.

Max Baucus, the U.S. ambassador to China, spoke about the matter Saturday with China's vice foreign minister to reiterate America's one-China policy on behalf of the current administration.

Chinese Foreign Ministry spokesman Lu Kang said Monday that China would have "no comment on what motivated the Trump team" to make the tweets, and he said he believed both sides would continue to support a "sound and a stable bilateral relationship."

But a commentary on the state-run Xinhua news agency issued a veiled warning.

"Succeeding a mostly upward U.S.-China relationship, Trump also needs to resist the light-headed calls for provocative and damaging moves on China by some hawkish political elites," said the commentary by Luo Jun. "The outdated zero-sum mindset is poisonous for Washington's foreign relations. It would be a mistake to think that Washington could gain from undercutting Beijing's core interests."

Stephen Yates, a former national security aide to Vice President Dick Cheney who has been in touch with Trump advisers, said the call with Tsai was arranged by the transition team and showed the president-elect wants to rebalance the U.S. relationship with China.

"He is not going to be told who he can or cannot talk to," Yates said by email as he flew to Taiwan for a trip he said was planned before the election. "He meant what he said about being open to leaders who seek good relations with the U.S. He knows more about these subjects than he might let on."

As a presidential candidate, Trump repeatedly accused China of manipulating its currency and trying to "rape our country" with unfair trade policies.

Walter Lohman, director of the Asian Studies Center at the conservative Heritage Foundation, said Trump appears to be signaling a willingness to increase ties with Taiwan, but not necessarily a full overhaul of U.S. policy.

"It doesn't mean we're going to poke the Chinese in the eye; it doesn't mean we're going to change the 'One China policy,'" said Lohman, whose think tank has been advising Trump's transition. "But it does mean we will reform our Taiwan policy to reflect reality."

AP