The Chinese researchers are believed to be affiliated with China's People's Liberation Army and left the USA after the Federal Bureau of Investigation conducted interviews in more than 20 cities and the State Department closed China's Houston consulate in July.

The op-ed comes after the U.S. has taken a series of actions against Beijing, which include imposing sanctions on Chinese officials, tariffs on Chinese goods and accusations against China during worldwide talks with third countries.

Outgoing US National Intelligence Director John Ratcliffe has warned that China is the biggest threat to the US and the free world.

The Trump administration, which once boasted of warm relations with China's President Xi Jinping, also has been ramping up sanctions against China over Taiwan, Tibet, trade, Hong Kong and the South China Sea.

He said he had shifted resources within the US$85 billion annual federal budget allocated to intelligence to increase the focus on China.

"Now let's all be honest about China", Ratcliffe told Reuters after the article was published.

Thursday's announcement adds to steps taken by President Donald Trump against China since losing his reelection bid November 3.

The move comes after President Donald Trump said in an executive order in November that China is increasingly exploiting US capital to enable the development and modernization of its military.

Trump's approach has taken relations between the world's two largest economies to their lowest point in decades and analysts say it could limit the incoming Biden administration's room for manoeuvre in dealing with Beijing. The department suspects the goods are produced with forced labor.

The nation's top intelligence official just unloaded on China in unusual fashion.

The Trump administration has only intensified its trade war with China before the president's expected departure from the White House, restricting travel visas for members of the Chinese Communist Party (CCP) and approving a bill to remove Chinese companies from USA exchanges if they fail to allow an audit of their finances. In his op-ed, he did not directly address the transition to a Biden administration. The executive order is meant to stop any USA capital from going to military-related Chinese companies on the blacklist.

"Beijing intends to dominate the USA and the rest of the planet economically, militarily and technologically", he said. Political analysts have said Trump was likely to take further action before President-elect Joe Biden takes office January 20.

On Wednesday, the USA said it would block imports from a major Chinese producer of cotton goods because of its reliance on workers detained as part of a crackdown on ethnic minorities in China's northwest.

China's foreign ministry said, "Their aim is to constrain and oppress relevant parties and enterprises in China and curb China's development".