The US government is set to extend its existing travel ban regime to around 80% of countries worldwide.
The US Department of State has confirmed it will launch a review of its current travel advisories this week.
It said this would likely result in a "significant increase" in the number of countries on its "do not travel" list
Updated advisories will "better reflect" the US Centers for Disease Control and Prevention’s (CDC) science-based travel notices, said the department.
These take into account issues affecting travellers’ health, as well as logistical factors such as in-destination testing availability and any current travel restrictions unique to US citizens.
"This update will result in a significant increase in the number of countries at Level 4: Do Not Travel, to approximately 80% of countries worldwide.
"This does not imply a reassessment of the current health situation in a given country, but rather reflects an adjustment in the State Department’s travel advisory system to rely more on CDC’s existing epidemiological assessments.
"As always, we are closely monitoring conditions around the globe, and will regularly update our destination-specific advice to US travellers as conditions evolve."
US citizens are being "strongly recommended" to reconsider all travel abroad owing to the "unprecedented risk" posed to all travellers by the pandemic.
UK residents are currently banned from travelling to the US, while the UK is already among countries on the US’s "do not travel" list due to Covid-19.
The move comes amid renewed hopes of US-UK travel corridor thanks to the pace of both countries’ Covid-19 vaccination programmes.
The UK government will reveal the countries making its "green list" early next month, which would allow travel without a return quarantine requirement.
There has not yet been any indication of which countries will make the list, but senior industry figures have talked up the prospect of the US being designated green.
Virgin Atlantic chief executive Shai Weiss told TTG last month he was hopeful of a resumption of UK-US travel this summer, while JetBlue is gearing up to launch its first London transatlantic programme this summer – suggesting confidence these trips will be possible without being subject to onerous travel restrictions.