The U.S. Department of Energy has said the coronavirus pandemic likely arose from a Chinese laboratory leak, a claim vehemently denied by Beijing on Monday.

The claim has also divided the different U.S. agencies as the White House maintained Sunday that American intelligence remained split on the issue.

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 FBI in believing that the pandemic, which has left nearly 7 million people dead, was the result of a mishap in a Chinese laboratory.

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

White House National Security Advisor 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 Sunday.

Beijing Monday called on those involved to "stop stirring up claims about laboratory leaks, stop smearing China, and stop politicizing the origin-tracing issue."

"A laboratory leak wasn't found to be possible by authoritative scientific conclusions drawn by joint experts from China and the WHO," Foreign Ministry spokesperson Mao Ning told a regular briefing.

In mid-February, the World Health Organization (WHO) pledged to do everything possible "until we get the answer" on COVID's origins, denying a report suggesting the agency had abandoned its investigation.

In a series of scientific papers published last July, researchers analytically identified Wuhan's Huanan Seafood Wholesale Market as the epicenter of the pandemic, conclusively denying other possibilities for the origins, particularly the conspiracy theories.

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.