US President Joe Biden has warned that the spread of Covid-19 misinformation on social media is "killing people".
He was responding to a question from a reporter about the alleged role of platforms like Facebook in spreading falsehoods about vaccines and the pandemic.
The White House has put increased pressure on social media companies to tackle disinformation.
Facebook said it was taking "aggressive action" to protect public health.
"They're killing people," Mr Biden told reporters at the White House yesterday. "The only pandemic we have is among the unvaccinated."
US health officials have warned that the country's current spike in Covid-19 deaths and infections is exclusively hitting unvaccinated communities.
Earlier yesterday, White House press secretary Jen Psaki said Facebook and other platforms were not doing enough to combat misinformation about vaccines.
"Obviously, there are steps they have taken," she said. "It's clear that there are more that can be taken."
A spokesperson for Facebook, Kevin McAlister, said the company would "not be distracted by accusations which aren't supported by the facts".
"We've removed more than 18 million pieces of Covid misinformation [and] removed accounts that repeatedly break these rules," the company said in a separate statement.
Facebook has faced criticism for its moderation - and misleading content about the pandemic is still widely available on its platforms.
Yesterday, US Centers for Disease Control and Prevention director Rochelle Walensky told reporters: "There is a clear message that is coming through: this is becoming a pandemic of the unvaccinated."
About 67.9 percent of US adults have received one dose of the vaccine, while 59.2 percent of adults are fully vaccinated.
Many eligible people refusing vaccinations in the US have said they do not trust them.
In March, a report said anti-vaccine activists on Facebook, YouTube, Instagram and Twitter had reached "more than 59 million followers, making these the largest and most important social media platforms for anti-vaxxers".
That same month, Mark Zuckerberg, Sundar Pichai and Jack Dorsey - the CEOs of Facebook, Google and Twitter respectively - were questioned in Congress over disinformation.
Dorsey told the senators that Twitter was committed to moderating posts. Pichai said YouTube worked to remove misleading content, and highlighted its role in relaying vaccine information.
Social media platforms admitted censoring revelations about politically embarrassing emails leaked from Biden's son's laptop in the run-up to last November's presidential election.
Twitter and Facebook blocked links to the New York Post reporting on Hunter Biden's dealings, after his father's campaign team claimed without evidence that it was "disinformation".
- BBC