Talks between US and Britain about a travel corridor are increasingly unlikely to reach a conclusion by the end of July, the Financial Times has reported.
Officials said the rise in cases of the Delta variant in Britain and uncertainty over the status of the AstraZeneca vaccine in the US, where it is not yet approved, were set to extend the talks into August and even September.
Authorities in London hoped they would have the outline of an agreement to reopen travel between the US and Britain by July 4, the paper reported.
Both countries established a working group "to help relaunch UK-US travel as soon as possible", a British government representative told Reuters.
"Discussions between the working group are ongoing to ensure the UK and US closely share thinking and expertise on international travel policy," they said.
Britain's Department of Transport was not immediately available for comment.
Earlier in June, US President Joe Biden and British Prime Minister Boris Johnson discussed opening a transatlantic travel corridor but no announcement was imminent, British Foreign Secretary Dominic Raab said.
On Monday, Spain announced that it would demand a negative Covid-19 test result or proof of vaccination from British tourists after letting them in freely for more than a month.
Portugal also announced British visitors must enter quarantine for 14 days from Monday if they are not fully vaccinated against Covid-19.