WASHINGTON — He praises enemies, he ignores allies, he upends decades of policy.

And Donald Trump hasn't even been sworn in as president.

In a series of telephone calls with foreign leaders apparently eager to congratulate the president-elect, Trump has broken many of the rules that govern delicate matters of international relations, leaving State Department diplomats shocked and confused.

The latest was Trump's decision Friday night to speak to the president of Taiwan, which no U.S. president or president-elect has done in nearly 40 years. The U.S. has no formal diplomatic relations with Taiwan, which China considers a rogue state and part of its national territory.

Already, China has lodged a formal complaint about Trump's call with Taiwanese President Tsai Ing-wen, though given the stakes of relations between the world's two superpowers, it tempered its reaction by emphasizing that Trump was not yet setting U.S. policy.

“The one-China policy” that does not recognize an independent Taiwan “is the cornerstone of the healthy development of China-U.S. relations, and we hope this political foundation will not be interfered with or damaged,” Chinese Foreign Minister Wang Yi said Saturday, blaming Tsai for playing a “small trick” on Trump.

The conversation had several of the hallmarks of Trump's most notable discussions with foreign leaders since being elected: unorthodox, out of step with current U.S policy and prompted by opaque motives.

“We've been taken by surprise at every turn,” one baffled national security staffer said of the calls to foreign leaders.

Trump offered no apologies, nor did his transition team make any comments. Instead, he defended the discussion amid reams of criticism for having broken U.S. protocol by saying Tsai initiated it.

“The President of taiwan CALLED ME today to wish me congratulations on winning the Presidency. Thank you!” Trump tweeted.

Later, Trump added: “Interesting how the US sells Taiwan billions of dollars of military equipment but I should not accept a congratulatory call.”

Under the Obama administration, the U.S. has sold $14 billion in weapons to Taiwan. The administration's Asia policy has centered on an effort to rebalance military and diplomatic resources toward the continent to counter the growing influence of China, though it has had limited success.

China was also one of Trump's frequent targets during the campaign, and the call could have been a first salvo in changing U.S. policy under the Trump administration. He wants to increase tariffs on China, has threatened to label the country a currency manipulator and blames it in part for the loss of jobs in the U.S.

But the sudden nature of the call with Tsai, without informing other interested parties such as China or the White House, unsettled foreign policy experts.

Trump's propensity to make and receive phone calls “heightens concerns about Trump's foreign policy deftness,” said Jeffrey Bader, a senior fellow at the Brookings Institution.

“There are serious risks posed by his failure to take briefings by government professionals,” Bader wrote in a blog post, “and he appears to have little respect for the potential damage of actions taken without understanding long-standing U.S. national security concerns.”

Trump's call with Tsai also prompted concern because his business empire is hoping to build in Taiwan.

Trump has said he'll step aside from operating the businesses during his presidency.

Beyond the conflicts of interest, however, Trump is ignoring U.S. policy.

In a telephone conversation with Pakistani Prime Minister Nawaz Sharif, Trump said Pakistanis were “exceptional people” and “one of the most intelligent people.”

The overtures belied Trump's attacks during the campaign on Pakistan as an evil sponsor of terrorism.

“You are a terrific guy,” Trump told Sharif, whom the U.S. regards as corrupt. “You are doing amazing work which is visible in every way.”

The U.S. has diplomatic relations with Pakistan, but considers India, Pakistan's arch-enemy, as a closer friend. Indians were shocked by Trump's blithely friendly tone with Sharif.

Trump has declined to receive most of the intelligence briefings he is entitled to as president-elect.

Trump does get information from the State Department, briefing books and other sources, senior adviser Kellyanne Conway told CNN after his phone call with Tsai.

The current administration has scrambled to emphasize that Trump's conversation with Tsai does not signal any change to long-standing U.S. policy, said Ned Price, a spokesman for the White House National Security Council.

Los Angeles Times' Christi Parsons contributed.

tracy.wilkinson@latimes.com