From Monday, travellers from the UK will need to test negative for coronavirus before boarding flights to the United States.
The new rule requires a negative test within 72 hours of departure, the Centers for Disease Control and Prevention said in a statement.
The restriction was imposed due to a new Covid-19 variant, said to be 70 percent more transmissible.
News of the strain led to nations around the world closing their borders to travellers from the UK.
“This additional testing requirement will fortify our protection of the American public to improve their health and safety and ensure responsible international travel,” CDC added.
The US in March halted the arrival of foreign nationals who had visited the UK in the preceding two weeks, which significantly cut air traffic from there.
Some airlines, including British Airways and Delta, had already agreed to require passengers test negative before departure to New York from Britain because of the new strain.
European Union governments have begun easing travel bans on the UK put in place to contain the variant, with nations being urged to reopen their borders with mandatory tests for arrivals.
The co-founder of BioNTech — one of the firms behind the vaccine that is being rolled out worldwide this week — has said its drug is “highly likely” to work against the mutated strain detected in Britain and otherwise can be adapted in six weeks.
