US authorities say the virus that caused the COVID-19 pandemic most likely leaked out of a Chinese research laboratory.

In an about-face on previous stances, the US Energy Department said new intelligence prompted it to conclude an accidental leak from a Wuhan lab – not as part of a weapons program – probably led to the global pandemic.

The Wall Street Journal reported the revelations on Sunday (US time), which it said came from an updated and classified 2021 US energy department study provided to the White House and senior American lawmakers.

The latest conclusion is an abrupt change on the department’s earlier position, which had been undecided on how the virus emerged.

The department joins the FBI in backing the lab-leak theory. Four other US agencies and a national intelligence panel believe the virus emerged through natural transmission, and two were undecided, the Journal wrote.

Officials briefed on the intelligence told the WSJ said that new evidence was relatively weak and that the Energy Department’s conclusion was made with “low confidence”.

The department had shared the information with other agencies, and none changed had their conclusions, officials said. Details of the new intelligence have not been revealed.

Reports out of the US suggest that a low-confidence assessment of intelligence means it is not reliable enough or is too fragmented to make a more definitive analytic judgment, or that there is not enough information available to draw a more robust conclusion.

In the US, Republican politicians seized on the new Energy Department conclusion and called for swift action against the Chinese government, which has refused to cooperate with global probes into the pandemic’s origin.

Tweet from @SenTomCotton

“Re. China’s lab leak, being proven right doesn’t matter,” tweeted Senator Tom Cotton, a long-time proponent of the theory the virus was linked to a lab in Wuhan that studies coronavirus.

“What matters is holding the Chinese Communist Party accountable so this doesn’t happen again.”

Another high-profile Republican, Marjorie Taylor Green tweeted “Conspiracy theorists – 100 Media – 0”. She has also publicly pushed the “lab leak” theory, as well as conspiracies about COVID vaccines.

Tweet from @RepMTG

Republican Senator Marsha Blackburn also tweeted her response, saying, “For years, Anthony Fauci and Biden officials called this a conspiracy.”

House Foreign Affairs Chairman Mike McCaul said on Sunday he was “pleased” that the Energy Department “has finally reached the same conclusion that I had already come to.”

“I have requested a full and thorough briefing from the administration on this report and the evidence behind it,” the Texas Republican said in a statement.

He called on the White House to publicly back the new conclusion.

“It is critical the administration also begin to work immediately with our partners and allies around the world to both hold the (Chinese Communist Party) accountable and to put in place updated international regulations to ensure something like this cannot happen again,” Mr McCaul said.

However, national security adviser Jake Sullivan said on CNN’s State of the Union that the intelligence community remained divided on the virus’ origins.

“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,” he said.

Mr Sullivan said President Joe Biden had put resources into getting a definitive answer.

The first COVID-19 cases were detected in the Chinese city of Wuhan in late 2019. The origins of the virus have been hotly debated since the early days of the pandemic.