Switzerland on Monday imposed an entry ban on arrivals from Britain and South Africa and ordered retroactive quarantine for all arrivals from the countries since December 14.
The federal government said the move was intended to stop tourism from countries following the discovery there of new, more contagious variants of Covid-19.
It stressed that the mutation had not been detected so far in Switzerland, which is already battling high and rising daily numbers of new coronavirus cases.
Swiss ski resorts are a top draw for European winter holidaymakers from Britain.]
"Following the discovery of a new, more contagious variant of the coronavirus in the UK and South Africa, the Federal Council today decided to take steps to prevent the further spread of this new virus strain," it said in a statement.
"All persons who have entered Switzerland from these two countries since December 14 must go into quarantine for 10 days.
"The Federal Council has also introduced a general entry ban from today for all foreign nationals seeking to enter Switzerland from the UK and South Africa. This is intended in particular to stop travel from these countries for tourism purposes."
Following a suspension announced on Sunday, the government said air travel between Switzerland and Britain and South Africa was now prohibited.
"A temporary derogation from the flight ban is being considered for persons resident in the UK or South Africa currently staying in Switzerland so that they may return home" -- and vice versa for Swiss residents," the government said.
"However, it is imperative that such return journeys do not lead to infections."
Switzerland also immediately withdrew freedom of movement privileges from British nationals, which were due to expire at the end of year in any case, as Britain leaves the European Union.
Switzerland is not in the EU but is part of the Schengen open-borders area.
"Persons from the UK are therefore subject to a general ban on entering Switzerland," it said.
The government added: "No cases of the new strain have so far been identified in Switzerland."