U.S. intelligence agencies said on Friday they may never be able to identify the origins of COVID-19, as they released a new, more detailed version of their review into whether the coronavirus was transmitted from animals to humans or was leaked from a lab.

The Office of the U.S. Director of National Intelligence (ODNI) said in a declassified report that a natural origin and a lab leak are both plausible hypotheses for how SARS-CoV-2 first infected humans. But it said analysts disagree on which is more likely or whether any definitive assessment can be made at all.

The report also dismissed suggestions that the coronavirus originated as a bioweapon, saying proponents of this theory "do not have direct access to the Wuhan Institute of Virology" and have been accused of spreading disinformation.

The report issued on Friday is an update of a 90-day review that U.S. President Joe Biden's administration released in August, amid intense political infighting over how much to blame China for the effects of the global pandemic rather than governments that may not have moved quickly enough to protect citizens.

Some U.S. spy agencies had strongly favoured the explanation that the virus originated in nature. But there has been little corroboration and in recent months the virus has spread widely and naturally among wild animals.

The ODNI report said four U.S. spy agencies and a multi-agency body have "low confidence" that COVID-19 originated with an infected animal or a related virus.

One agency said it had "moderate confidence" that the first human COVID-19 infection most likely was the result of a laboratory accident, probably involving experimentation or animal handling by the Wuhan Institute of Virology.

U.S. spy agencies believe they won't be able to produce a more definitive explanation for the origin of COVID-19 without new information demonstrating that the virus took a specific pathway from animals to humans or that a Wuhan laboratory was handling the virus or a related virus before COVID-19 surfaced.

The report said U.S. agencies and the global scientific community lacked "clinical samples or a complete understanding of epidemiological data from the earliest COVID-19 cases" and said it could revisit this inconclusive finding if more evidence surfaces.

China has faced international criticism for failing to co-operate more fully in investigations into the origins of the virus. China's embassy in Washington did not immediately respond to a request for comment.