Dr Anthony Fauci, the top US infectious disease expert, has apologised for remarks that seemed to criticise the UK's vaccine approval process.
"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. He later told CBS News that the UK had "rushed" the approval, BBC reported.
On Thursday, he walked back the comments, and said there was "no judgement on the way the UK did it".