The US will restrict travel from South Africa and seven other southern African countries to try to contain a new coronavirus variant spreading there.
From Monday, only US citizens and residents will be allowed to travel from the region.
This follows a similar flight ban imposed by the EU and the UK. Canada is also introducing travel restrictions.
The World Health Organization (WHO) earlier declared the new variant to be "of concern", naming it Omicron.
US officials said flights from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi will be blocked, mirroring earlier moves taken by the EU. The ban will come into effect on Monday.
In a statement, President Joe Biden called the move a "precautionary measure" taken until more is known about the variant.
Canada is also shutting its borders to foreign travellers who have recently been to South Africa, Namibia, Lesotho, Botswana, Eswatini, Zimbabwe and Mozambique. Foreign citizens will be banned from Canada if they have been to the seven nations in the past 14 days.