News of his departure was first reported by Radio Free Asia.

Schriver’s nearly two-year tenure has been marked by his persistent critique of Beijing’s policies and behaviour in the military and security spheres and his view of strategic competition between the US and China as “the defining challenge of our generation”.

In May, Schriver became the first US official to publicly use the term “concentration camps” to describe the mass internment facilities in China’s far west, where the United Nations estimates that up to 1 million Uygurs and members of other ethnic minority groups have been detained and subject to forced indoctrination.

Such remarks put the US official at loggerheads with Beijing’s foreign ministry, which accused him of “grossly interfering” in China’s internal affairs and called on him to “respect the truth and put aside [his] prejudices”.

Schriver’s policy initiatives also caused friction closer to home, according to a report in Foreign Policy that cited unidentified sources.

His efforts to strengthen relations with Taiwan, the self-governing island that Beijing considers part of its territory, ran counter to US President Donald Trump’s attempts to conclude a trade agreement with China, causing Schriver to be “frustrated”, the report said.

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Regardless, Schriver’s policies would not be easily overturned, said James Carafano, vice-president of foreign and defence policy at the Heritage Foundation, a Washington-based think tank.

Schriver “had a huge impact in terms of freedom of navigation [in the South China Sea], shifting resources to the Indo-Pacific theatre, elevating US-Japan-Australia and Indian relations and US-India relations”, Carafano said.

“He had big impact in focusing US policy on countering China military inputs in the Indo-Pacific.

“The policies that Schriver set will drive on because he got the train going down the tracks and it’s just going to keep going.”

Before his appointment in early 2018, Schriver had worked in a number of government, military and civilian positions relating to East Asian affairs.

They included deputy assistant secretary of state for East Asian and Pacific affairs, CEO and president of the Project 2049 Institute, a think tank focused on security in Asia, and attache for the navy at the US embassy in Beijing.

In a previous stint at the Pentagon in the mid-1990s, Schriver handled the US military’s relations with China’s People’s Liberation Army and oversaw the military relationship with Taiwan.

During his most recent posting, Schriver was considered a fervent ally of Taipei in the face of what he called rising pressure from Beijing in the form of military build-up and activities in the region.

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In June, during a discussion at the Washington-based Heritage Foundation, he said the US would treat Taiwan “as a normal security assistance partner” when it came to arms sales.

Taiwan – and the United States’ policy of assurance towards the island – would be the area where Schriver’s departure would be most heavily felt, said Mira Rapp-Hooper, senior fellow for Asia studies at the Council on Foreign Relations.

“No one will match his experience working on this issue,” she said.

Emphasising that she had no first-hand knowledge of the events that led to his resignation, Rapp-Hooper said: “Rapid turnover in Pentagon leadership and endemic foreign policy dysfunction at other agencies, are, however, totally inimical to the implementation of coherent US strategy for China and Asia.”

The Pentagon’s National Defence Strategy of 2018, which identified China as a strategic competitor seeking to shape a world consistent with its “authoritarian model”, was far from implemented, she said, “and the prospects of its realisation dim a bit further with Schriver’s departure”.