WASHINGTON — Whether by accident or design, President-elect Donald Trump is signaling a tougher American policy toward China, sparking warnings from both the outgoing Obama administration and Beijing.

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 Obama’s deliberative 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 cybertheft of U.S. commercial secrets, the two powers have cooperated effectively on climate change and the Iran nuclear deal.

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.