The White House said Monday that it didn't understand why Donald Trump upended nearly 40 years of U.S. foreign policy by speaking to Taiwan's president.

Trump bit into the forbidden fruit on Friday when he accepted a call from Taiwan's Tsai Ing-wen. His transition team is officially saying it was a 'courtesy'.

A Washington Post report says Trump was spoiling for a fight with China.

'I think it's hard to determine exactly what the aim was of the president-elect,' White House Press Secretary Josh Earnest said today.

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White House press secretary Josh EArnest said Monday that the Obama administration doesn't understand why Donald Trump upended nearly 40 years of U.S. foreign policy by speaking to Taiwan's president

The Obama administration official warned Trump that he risked damaging U.S. interests and creating unrest in the Taiwan Strait, which separates the island from the mainland, with the gesture.

'Some of the progress that we have made in our relationship with China could be undermined by this issue flaring up,' Earnest said.

It is also 'unclear' how it helps the people of Taiwan, he stated. Already, it has provoked China to 'ratchet up' its rhetoric against Taiwan, which is also the United States' ninth-largest trading partner.

'These are significant issues,' he said, 'and worthy of careful consideration.'

The White House says two national security officials in the U.S. talked to their counterparts in Beijing and restated the Obama administration's commitment to its one-China policy.

'The Chinese government and senior officials in the Chinese government are sophisticated enough to understand the complexities in the U.S. political system,' he said. 'Our message...was intended to make clear that the policy position of the Obama admin had not changed.'

Trump said in a four-tweet statement that Tsai called him.

He used the occasion to whack China, saying the country devalues its currency and built 'a massive military complex in the middle of the South China Sea' without U.S. permission. 'I don't think so,' he added.

Vice president-elect Mike Pence said Sunday that the incident was overblown.

'She reached out to the president-elect and he took the call from the democratically elected leader of Taiwan,' he said on Meet The Press. 'I think most Americans, and frankly most leaders around the world, know this for what it was.'

Donald Trump, pictured, accepted a phone call of congratulations from Taiwan's President Tsai Ing-wen on Friday and it has caused diplomatic issues with the Beijing

Trump claimed on his Twitter feed that the Taiwanese government had called him. His vice president said he took the call as a 'courtesy'

Pence said it was a 'courtesy' call and Trump intends to 'engage the world on America's terms.'

'It's striking to me that President Obama would reach out to a murdering dictator in Cuba and be hailed as a hero,' he said. 'And President-elect Donald Trump takes a courtesy call from the democratically-elected president of Taiwan and it becomes something of a thing in the media.'

Earnest referred to Pence's statements today and the conflicting portrait presented in the Washington Post. The publication claimed Trump had been planning the move since before he became the Republican nominee for president.

'It's unclear exactly what this strategic effort is, what the aim of this strategic effort is,' the Obama spokesman said. 'And it's unclear exactly what potential benefit could be experienced by the United States, China or Taiwan. But I'll leave that to them to explain.'

Trump responded to criticism of the phone call with an attack on China

China rebuked Trump through the official publication of its Communist Party for taking the call - the first conversation between a U.S. leader and Taiwan since 1979.

The overseas edition of the People's Daily said 'creating troubles for the China-U.S. relationship is creating troubles for the U.S. itself' and Trump 'would greatly reduce the chance to achieve the goal of making America great again' if he continues down this path.

China's foreign ministry spokesman, Lu Kang, said Monday that his county had launched 'stern representations with the relevant side in the U.S.' but would not say who officials spoke to, Reuters said.