A war of words between the United States and China over coronavirus intensified on Monday after the Chinese embassy in France suggested the outbreak actually started in the US.

President Donald Trump and other American officials have repeatedly described coronavirus as the "Chinese virus", incensing Beijing and sparking tit-for-tat accusations on the origin of the contagion.

More:

"How many cases of COVID-19 were there among the 20,000 deaths due to the flu that started [in the US] in September last year?" the Chinese embassy in Paris asked in a string of messages on Twitter.

"Did the United States not try to pass off pneumonia due to the new coronavirus as flu?"

The embassy did not point to any scientific evidence for its claims.

China's embassy in France also described the "surprise closing last July of the largest American biochemical weapons research centre at the Fort Detrick base in Maryland".

"After the closure, a series of pneumonia or similar cases appeared in the United States," it alleged.

Iran accusations

Iran's Supreme Leader Ayatollah Ali Khamenei claimed on Sunday that the coronavirus could be man-made by the US government.

The virus "is specifically built for Iran using the genetic data of Iranians, which they have obtained through different means", he said.

Calling COVID-19 the "Wuhan virus", US Secretary of State Mike Pompeo on Monday said Khamenei's "fabrications are dangerous".

"He works tirelessly to concoct conspiracy theories and prioritises ideology over the Iranian people," Pompeo said of the supreme leader.

Trump and Pompeo have angered Beijing by repeatedly referring to "the Chinese virus" when discussing the COVID-19 outbreak first detected in the Chinese city of Wuhan.

Earlier this month, a foreign ministry spokesman in Beijing, Zhao Lijian, suggested in a tweet the US military brought the virus to Wuhan.

The US in response summoned China's ambassador, accusing China of "spreading conspiracy theories" and of "seeking to deflect criticism for its role in starting a global pandemic and not telling the world".