Dr Anthony Fauci, the top US infectious disease expert, has apologised for remarks that seemed to criticise the UK's vaccine approval process, BBC reports.
"I have a great deal of confidence in what the UK does both scientifically and from a regulator standpoint," Dr Fauci told the BBC on Thursday.
The UK on Wednesday became the first country in the world to approve the Pfizer vaccine for the coronavirus.
It has defended the rapid approval and said the jab is safe and effective.
Dr Fauci on Wednesday had told Fox News that the UK did not review the vaccine "as carefully" as US health regulators, although he implied that the US would quickly also be in a position to approve a vaccine. "We'll be there. We'll be there very soon," he added.
He later told CBS News that the UK had "rushed" the approval, but on Thursday he walked back the comments, and said there was "no judgement on the way the UK did it".
"Our process is one that takes more time than it takes in the UK. And that's just the reality," Dr Fauci told the BBC. "I did not mean to imply any sloppiness even though it came out that way."
The UK has ordered 40 million doses of the Pfizer/BioNTech coronavirus vaccine - enough to vaccinate 20 million people, and the first consignment of that vaccine has now arrived.
