Passengers from the United Kingdom will have to quarantine for 14 days after arriving in Portugal if they are not fully vaccinated against COVID-19, the Portuguese government said in a statement late Sunday.

The new rule, which is set to take effect as of Monday and will remain in place until at least July 11, comes amid a surge in cases in Portugal, where the number of daily new COVID-19 infections is back to February levels when the country of just over 10 million was still under a strict lockdown.

Daily positive cases have also been rising in Britain for a month.

Britons arriving in Portugal by air, land or sea must show proof they are fully vaccinated or self-isolate for 14 days at "home or at a place indicated by health authorities," the government said in a statement.

Britain, one Portugal's biggest sources of foreign tourists, removed the southern European destination from its quarantine-free travel list earlier this month. Germany declared Portugal to be a "virus-variant zone" last week, a measure that will trigger severe restrictions on travel to and from the country.

Portugal, which faced its worst battle against the coronavirus earlier this year, is on Britain's amber list, meaning holidaymakers must self-isolate for 10 days when they return home and take expensive COVID-19 tests.

Portuguese health authorities have blamed the more contagious Delta variant, first identified in India but rapidly spreading in Britain too, for the recent rise in infections. Over 70% of COVID-19 cases in the Lisbon area are from the delta variant.