A laboratory leak was the most likely origin of the COVID-19 virus, according to findings by the U.S. Energy Department, The Wall Street Journal reported.

A classified intelligence report provided to the White House and key members of Congress said the virus likely spread due to a mishap at a Chinese laboratory, The Journal reported on Sunday.

The Energy Department had previously been undecided on the source of the virus. The conclusion is due to new intelligence, but the department made its judgment with “low confidence,” according to people who have read the classified report, The Journal said.

U.S. national security adviser Jake Sullivan said Sunday there’s “a variety of views” in the U.S. intelligence community about whether the virus originated naturally or in a lab and he “can’t confirm or deny” the Wall Street Journal report.

President Joe Biden has asked the National Laboratories, which are part of the Energy Department, to be part of the assessment, Sullivan said on CNN’s “State of the Union.”

“And if we gain any further insight or information, we will share it with Congress and we will share it with the American people,” he said. “But, right now, there is not a definitive answer that has emerged from the intelligence community on this question.”

China has long hit back at any suggestion that the COVID-19 virus originated in a lab. The Chinese Embassy in Washington didn’t immediately respond to a request for comment outside regular working hours.