Joe Biden has called for an international investigation to establish whether Covid-19 leaked from a Chinese laboratory as he tried to rally G7 leaders behind a "competition with autocracies".
But his remarks about a "lab leak" on Sunday were played down by other leaders and the G7 summit broke up without bridging major rifts over China.
The leaders of Canada, France, Germany, Italy, Japan, Britain and the United States called for the World Health Organisation to convene a "a timely, transparent, expert-led, and science-based” investigation into the origins of Covid-19, “including in China,” in a joint statement issued after three days of talks on Sunday.
In comments that will infuriate Beijing, Mr Biden said neither he nor US intelligence had reached a conclusion about whether the virus had come from a laboratory but said he wanted to establish a "bottom line" for transparency as part of measures to prevent another pandemic.
“Transparency matters across the board. We haven’t had access to laboratories to determine whether or not… this was a consequence of [the] market place and the interface with animals and the environment, or whether it was an experiment gone awry in a laboratory,” Mr Biden said.
Boris Johnson said it was “unlikely" the coronavirus pandemic emerged from a lab, but added: “Clearly anyone sensible would want to keep an open mind on that.”
Emmanuel Macron, the French president, said “there was no discussion among leaders on the origins of the virus" and dismissed the theory as a distraction from combating the disease.
Mr Macron said the G7 was not a club that was hostile to China, despite differences over human rights.
The disagreement reflected broader rifts over how far to go in confronting China over human rights and strategic competition.
Mr Biden arrived in Cornwall seeking strong language condemning China’s human rights record and a more direct recognition of the global struggle for influence between the West and Beijing.
He explicitly framed an agreement to create a “build back better” green-infrastructure programme for developing countries as a competitor to China’s Belt and Road Initiative and demanded condemnation of China’s use of Uyghur muslims as forced labour in clothes factories.
But he faced significant pushback from European allies, especially Mr Macron, who did not want to portray the group as “hostile” to China.
The final communique called on China to "respect" human rights in Xinjiang and Hong Kong and separately condemned the use of forced labour in global supply chains, but made no reference to Uyghur prison labour.
It also underscored the “importance of peace and stability across the Taiwan Strait” rather than criticising China for aggressive behaviour.
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Mr Biden declared himself "satisfied" with the outcome of the talks.
"We’re in a contest with autocrats and autocratic governments around the world as to whether or not democracies can compete with them in a rapidly changing 21st century," he said. "I have walked away from the meeting with all my colleagues and believe me, they are convinced that is correct," he added.
The UK, US, Canada and EU in March announced a raft of sanctions against Chinese officials for human rights violations in Xinjiang.
Rifts over China were already apparent long before the leaders arrived in Cornwall on Thursday.
Mr Johnson, who hosted the summit, initially proposed forging a semi-formal "D10" group of democracies with guest powers Australia, India, South African and South Korea in what critics called a thinly-veiled attempt to build an anti-China alliance.
The idea was dropped following objections from France, Germany and Japan.