Italy warned England soccer fans they shouldn't count on being allowed into the Stadio Olimpico for the European Championship quarterfinal match against Ukraine on Saturday unless they can prove they have observed five days of quarantine after arriving.

The warning, posted on the website of the Italian embassy to Britain, made clear that even if they have tickets, proof of vaccination and negative Covid-19 tests, fans should "not travel to Italy to attend the match".

It wasn't immediately clear how Italy could enforce the warning, given authorities have never policed quarantine requirements during the coronavirus pandemic and don't put visitors in quarantine hotels, as some other countries do.

Currently, Italian regulations require a five-day quarantine for anyone who has been in Britain in the previous 14 days. The statement repeated that requirement but, in a clear effort to dissuade people from coming or trying to get around it, suggested fans would be policed and prevented from getting into the stadium even if they have tickets.

"Only those who can prove that they have arrived in Italy at least six days previously, have observed five days of quarantine, and have taken a post-quarantine Covid-19 test with a negative result will be allowed into the Stadio Olimpico," the statement said, adding that even people who have legal exemptions to avoid the quarantine, such as for brief work trips to Italy, would similarly not be allowed into the stadium.

Italy, where Europe's outbreak erupted last year, has tamed the latest wave of infections and has fully vaccinated nearly 35% of its population over the age of 12. Currently, the highly contagious delta variant spreading through Britain represents about 17% of the new cases in Italy, but officials are warning that it will likely become dominant by August.