A Chinese foreign ministry official pushed a conspiracy theory the US army may have had a role in spreading the novel coronavirus, highlighting growing tensions between the world's biggest economies as both governments seek to deflect blame for the outbreak.
"It might be US army who brought the epidemic to Wuhan," Zhao Lijian, a foreign ministry spokesman, said in a tweet. "Be transparent! Make public your data! US owe us an explanation!"
He later followed up with another tweet urging his 284,000 followers to share an article arguing that the virus originated in the US. It was posted on a website promoting conspiracy theories, including articles lambasting the "Vaccine Deep State" and questioning whether Osama bin Laden ever existed.
On Friday in Beijing, Geng Shuang, another spokesman for the foreign ministry, said that "international society, including the US, has different opinions about the source of the virus. But China always believes that this is a matter of science which requires professional and scientific assessment."
Geng was asked twice if the earlier tweets by his colleague, Zhao, represented the view of the Chinese government. "I think you may want to ask certain senior US officials - did they speak on behalf of the US government when they attacked and smeared China recently?" he said in response to one question.
"What I said represents the Chinese government's attitude," he said, in response to the other.
With the coronavirus spreading from China into the US and around the world, both nations are trading tit-for-tat claims about its origins. While it's unclear whether Zhao was being facetious, earlier this month he became the first official in China to suggest the virus didn't originate there, even though he hasn't provided any evidence for that claim.
Asked about the claim, Geng had said earlier this week "the origin of the virus can only be determined by science" and expressed hope the issue would not be used to "stigmatise" any country.
The US State Department didn't immediately respond to a request for comment.
President Donald Trump, who is facing an election this year, has sought to blame China for the virus as the outbreak slams global stock markets and threatens to push the world into recession. In a major prime time television address about the virus on Wednesday night, Trump made numerous references to China, referred to the disease as a "foreign virus" and said "sweeping travel restrictions on China" imposed by the US had prevented the scale of outbreaks now seen in Europe.
"It started in China and is now spreading throughout the world," Trump said.
This isn't Zhao's first controversy on Twitter. While serving as China's deputy chief of mission at its embassy in Islamabad in July, he posted a string of messages aimed at highlighting US hypocrisy in criticising Beijing's human rights record at a time when Washington was ramping up criticism of detention camps in western China's Xinjiang province.
Zhao mentioned everything from school shootings and income inequality to racial segregation, adding that if "you're in Washington, DC, you know the white never go" to the Southeast part of the US capital, home to historically African-American areas. That tweet, which he later deleted, drew the attention of former US National Security Adviser Susan Rice, leading to an heated online argument.
"You are a racist disgrace. And shockingly ignorant too," Rice tweeted at Zhao. Probably on the assumption that Zhao was based at China's mission in Washington, she also addressed the Chinese ambassador to the US, Cui Tiankai, who had recently joined Twitter. "Ambassador Cui, I expect better of you and your team. Please do the right thing and send him home."