The determination – noted in a classified report by director of national intelligence Avril Haines’s office, The Wall Street Journal reported – marks a shift by the energy department, which had previously said it was undecided on how the virus emerged.

People who read the classified report were quoted in the Journal and The New York Times as saying the department made its judgment with “low confidence”, highlighting how different agencies remain divided over the origins of Covid-19 and the pandemic that swept the globe in early 2020.

The conclusion, reportedly the result of new intelligence, is nevertheless significant because the department oversees a network of national laboratories, including some that do advanced biological research.

The department now joins the Federal Bureau of Investigation in believing that the pandemic, which has left nearly seven million people dead, was the result of a mishap in a Chinese laboratory.

Four US intelligence agencies believe Covid occurred through natural transmission, while two others remain undecided, the Journal reported.

White House national security adviser Jake Sullivan stressed a “variety of views” on the matter remain.

“Right now, there is not a definitive answer that has emerged from the intelligence community on this question,” he told CNN yesterday.

Beijing today called on those involved to “stop stirring up claims about laboratory leaks, stop smearing China, and stop politicising the origin-tracing issue”.

“A laboratory leak wasn’t found to be possible by authoritative scientific conclusions drawn by joint experts from China and WHO,” foreign ministry spokesman Mao Ning told a regular briefing.

In mid-February, the World Health Organization pledged to do everything possible “until we get the answer” on Covid’s origins, denying a report suggesting the agency had abandoned its investigation.

The scientific community sees it as crucial to determine the origins of the pandemic in order to better fight or even prevent the next one.