Tourists this month in Dresden, Germany. The new classification is part of a weekly assessment done by German officials based mostly on infection rates in other countries.Credit...Robert Michael/picture alliance, via Getty Images

After weeks of being able to visit Germany relatively easily, American tourists and other nonessential travelers will have to quarantine for 10 days, starting Sunday, if they cannot document full vaccination or immunity from a past infection. They can shorten their quarantine with a negative test on the fifth day.

The new classification is part of a weekly assessment done by German officials based mostly on infection rates in other countries. Turkey and Israel were also reclassified as high risk.

Coronavirus cases in the United States — which reported 186,840 new cases on Friday — have steadily risen since early July, driven largely by the more contagious Delta variant of the virus. Germany has averaged about 3,000 new cases per day in the past seven days, according to a New York Times database.

Germany had reopened its borders to tourists from the United States in late June, after more than a year of a complete ban on nonessential travelers from most countries outside the European Union. The United States has maintained its ban on European travelers since the early days of the pandemic.