The United States announced Friday it is restricting travel from eight southern African countries over fears of a new variant of Covid-19 detected in South Africa.

Travel will be mostly banned starting Monday from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi, a senior official in President Joe Biden's administration said.

Only US citizens and permanent residents will still be able to travel from the eight countries, the official, who spoke on condition of anonymity, added.

"The policy was implemented out of an abundance of caution in light of a new Covid-19 variant circulating in Southern Africa," the official said.

"Our scientists and public health officials are working quickly to learn more about this variant," the official added.

"President Biden has promised to take every measure necessary to keep Americans safe and defeat the pandemic, and this was a step recommended by US government medical experts and the Covid-19 Response Team."