Israel warned on Tuesday against travel to the United States and other countries and said it would tighten quarantine measures for inbound travelers as part of efforts to slow the spread of the coronavirus Delta variant.

It also began mandating isolation for returning travelers - including those vaccinated or recovered from the virus - from countries deemed "red", indicating a rapid spread of the disease.

On Tuesday, the health ministry said it would add 18 countries to its red list, including the United States, France, Italy, Iceland, Greece, and others.

"Beginning August 11, 2021, complete isolation for all age groups is required, even for the vaccinated and recovering," the health ministry said of the 18 countries, warning of "a significant increase in morbidity coming from abroad".