Its public health agency updated its criteria on Monday, which saw 61 countries lowered from a Level 4 "avoid all travel" rating.

Countries such as France, Spain and Italy are now Level 3, which means fully-vaccinated passengers may go to these areas.

But most passengers from the UK are still banned from travelling to the US.

Although the UK is listed as a Level 3 by the US Centers for Disease Control and Prevention (CDC), under a presidential decree introduced last March, non-US citizens who have been in the UK in the last 14 days cannot enter the country unless a specific exemption applies.

Meanwhile, travellers from the US to the UK must self-isolate for 10 days on arrival as the country is on the "amber list".

The US Centers for Disease Control and Prevention said that it had updated its criteria to "better differentiate countries with severe outbreak situations from countries with sustained, but controlled, Covid-19 spread."

The CDC said the new criteria for a Level 4 "avoid all travel" recommendation has changed from 100 cases per 100,000 to 500 cases per 100,000.

Other countries that saw their ratings lowered include:

*  Ecuador
*  Philippines
*  South Africa
*  Canada
*  Mexico
*  Russia
*  Switzerland
*  Jordan
*  Denmark
*  Turkey
*  Ukraine
*  Honduras
*  Hungary

Japan also saw its travel rating lowered to allow vaccinated passengers to travel in the run-up to the Tokyo Olympics in late July. On 24 May, the State Department had issued a warning against the country, citing a new wave of Covid-19 cases.

The CDC said it also expects more countries to get lower ratings in the coming weeks.

It comes after the bosses of all airlines that offer UK-US flights and Heathrow Airport issued a joint call for a trans-Atlantic travel "corridor" on Monday.

The group said it would be "essential to igniting economic recovery" in a statement and urged Prime Minister Boris Johnson and President Joe Biden to discuss the possibility at the upcoming G7 meeting.

Shai Weiss, the boss of Virgin Atlantic, said on Monday: "There is no reason for the US to be absent from the UK green list. This overly cautious approach fails to reap the benefits of the successful vaccination programmes in both the UK and the US."

Adding the US to the green list would remove the need for quarantine on return to the UK. Passengers would, however, still need to have proof of a negative Covid test result on departure.

"Customers, families and businesses need to book and travel with confidence. After 15 months of restrictions, the time to act is now," Mr Weiss added.