Officials involved in talks about a transatlantic travel route said it was "increasingly unlikely" they would reach a conclusion by the end of next month, according to the Financial Times.
A combination of the spike in cases of the Delta variant in the UK, "complexities" in the US political system and the uncertainty over the AstraZeneca vaccine are said to be the reasons behind the possible delay.
Talks could be extended into August and September.
On Monday (28 June), Portugal, the Balearic Islands and Hong Kong announced tighter restrictions on travellers entering from the UK.
