A US House of Representatives panel investigating the coronavirus pandemic held its first hearing on Wednesday, further highlighting continued disagreement on the origins of Covid-19.
The bipartisan subcommittee under the committee on oversight and accountability was created in April 2020 to oversee the pandemic response by the administration of Donald Trump.
After Republicans gained a majority in the House, the group was given the task of focusing on where the virus may have emerged from.
The US Department of Energy last month said the coronavirus probably came from a Chinese laboratory leak, although that assessment was made with "low confidence".
Republican members spoke about being called "conspiracy theorists" for investigating the lab leak possibility, while Democrats opposed politicising science.
“Today’s hearing marks a concerning step down the path of letting extremism get in the way of an inquiry that should be led by science and facts,” said Raul Ruiz, the Democrats' ranking member on the committee.
Three witnesses, including Dr Robert Redfield, the former director for US Centres for Disease Control and Prevention, suggested Covid-19 may have leaked from a laboratory in Wuhan, China, in the past but testified on Wednesday that there is no definite answer.
Meanwhile, chiefs of US intelligence agencies testifying in a Senate hearing about worldwide threats continued to claim that the intelligence community could not definitely establish virus origins, to the frustration of senators.
Most leading medical organisations say Covid-19 emerged naturally.
The World Health Organisation says finding the origin is important in fighting Covid-19 and for future pandemic prevention.