US President Joe Biden on Monday toned down his comments about Facebook after accusing it of "killing people" by not stopping Covid vaccine misinformation, but he still urged the world's largest social network to do more.

"We are not in a war or in a battle with Facebook, we are in a battle with the virus," White House Press Secretary Jen Psaki told reporters.

Her remarks followed the president's own comments essentially walking back his blunt outburst from Friday.

"Facebook isn't killing people," Biden stressed in response to a reporter asking about the flap.

Biden added that he had learned a dozen people were largely responsible for disseminating false news about the vaccines.

"These 12 people who are out there giving misinformation -- anyone listening to it is getting hurt by it. It's killing people. It's bad information," Biden said.

"My hope is that Facebook, instead of taking it personally -- that somehow I'm saying Facebook is killing people -- that they would do something about the misinformation, the outrageous misinformation about the vaccine," he said.

"That's what I meant."

Biden had delivered an unusually harsh rebuke last week when he assailed Facebook's handling of widely spread misinformation about vaccinations and said "this is becoming a pandemic of the unvaccinated."

His administration piled on, urging the company to react more quickly in taking down problematic posts.

Facebook, which has contracted outside fact checkers in an effort to clean up its content, quickly fired back at the White House on Friday, with a company spokesperson saying "the facts show that Facebook is helping save lives. Period."

Concerned that the US vaccination campaign is bogged down just as the dangerous Delta variant is causing an surge in new infections, the White House last week notably toughened its tone against tech giants, calling on them to boost the fight against misinformation.