The virus which drove the Covid-19 pandemic most likely emerged from a laboratory leak but not as part of a weapons program, according to an updated and classified 2021 US energy department study provided to the White House and senior American lawmakers, the Wall Street Journal reported on Sunday.

The department’s finding – a departure from previous studies on how the virus emerged – came in an update to a document from the office of National Intelligence director Avril Haines. It follows an FBI finding, issued with “moderate confidence”, that the virus spread after leaking out of a Chinese laboratory.

The conclusion from the energy department – which oversees a network of 17 US laboratories, including areas of advanced biology – is considered significant despite the fact that, as the report said, the agency made its updated judgment with “low confidence”.

Conflicting hypotheses on the origins of Covid-19 have centered either on an unidentified animal transmitting the virus to humans or its accidental leak from a Chinese research laboratory in Wuhan.

The spread of Covid-19, just one in a line of infectious coronoviruses to emerge, caught global health bodies unawares in early 2020. It has since caused close to 7 million deaths worldwide, according to the World Health Organization, and disrupted trade as well as travel.

Former US president Donald Trump politicized the issue, calling it the “China virus”, triggering a racialization of a pandemic that his Democratic successor Joe Biden has sought to avoid. But political polarization remains under the surface of efforts to establish its origins.

The energy department’s updated findings run counter to reports by four other US intelligence agencies that concluded the epidemic started as the result of natural transmission from an infected animal. Two agencies remain undecided.

US officials, the Journal said, also declined to expand on new intelligence or analysis that led the energy department to change its position. They also noted that the energy department and FBI arrived at the same conclusion for different reasons.

The CIA remains undecided between leak and natural transmission theories, according to the National Intelligence Council study. But while the initial 2021 report did not reach a conclusion, it did offer a consensus view that Covid-19 was not part of a Chinese biological weapons program.

The National Security adviser, Jake Sullivan, acknowledged Sunday that there are a “variety of views” within US intelligence agencies on the issue.

“Some elements of the intelligence community have reached conclusions on one side, some on the other, and a number have said they just don’t have enough information to be sure,” Sullivan told CNN.

But he said that the Biden administration has “directed repeatedly every element of our intelligence community to put effort and resources on getting to the bottom of this question”.

Sullivan added that Biden had specifically requested that the National Laboratories under the energy department be brought into the assessment. “He wants to put every tool at use to figure out what happened,” Sullivan said.

“Right now there is not a definitive answer to emerge from the intelligence community on this question,” he added, referring to eight of 18 agencies – along with the National Intelligence Council – that have looked in Covid-19s origins.

A previous report by the energy department’s Lawrence Livermore National Laboratory in May 2020 concluded that a lab-leak theory was plausible.

The updated, five-page NIC assessment, the Journal reported, “was done in light of new intelligence, further study of academic literature and consultation with experts outside government” and comes as Republicans in Congress press for more information.

A spokesperson for the energy department wrote in a statement that the agency “continues to support the thorough, careful, and objective work of our intelligence professionals in investigating the origins of Covid-19, as the president directed”.

Chinese officials have disputed that Covid-19 could have leaked from its labs, among them the Wuhan Institute of Virology, the Chinese Center for Disease Control and Prevention, (CDC) and the Wuhan Institute of Biological Products.

According to the initial US 2021 intelligence report, Covid-19 first circulated in Wuhan, China, no later than November 2019, when three researchers from the Wuhan Institute of Virology – reportedly involved in coronavirus research – were sick enough to seek hospital care.