Burundi and Rwanda have been added to the “red list” of countries from where travel to the UK is banned.
The measure, aimed at stopping the spread of the South African variant, comes into force from 13:00 GMT on Friday.
British, Irish and third country nationals with residence rights in the UK will be allowed to enter but must self-isolate for 10 days at home.
UK Transport Minister Grant Shapps said passengers allowed to enter the country would need proof of a negative test and a completed passenger locator form before arrival, or could face two £500 ($684) fines.
Last week, the Rwandan authorities imposed a 15-day lockdown in the capital, Kigali, to limit a second wave of coronavirus cases. The restrictions will end next Tuesday.
January has been the deadliest month for the East African country. The authorities say more than half of the total deaths were recorded this month, as well as one third of the total 13,885 cases.
Earlier this month, Burundi closed its land and water borders to contain the spread of the virus.
BBC