In updates posted to the agency's website on Monday, the CDC added Greece, Ireland, the U.S. Virgin Islands, Iran, Andorra, Curacao, Gibraltar, Guadeloupe, Isle of Man, Kazakhstan, Lesotho, Libya, Malta, Martinique, Saint Barthelemy and Saint Martin to "Level 4," marking areas with the highest level of coronavirus risk.
"Avoid travel to these destinations. If you must travel to these destinations, make sure you are fully vaccinated before travel," the CDC warns above the list of 70 countries.
The advisories are based on a scale of five tiers including Low (1), Moderate (2), High (3), Very High (4) and Unknown.
The CDC also advises that individuals who are unvaccinated avoid nonessential travel to Level 3 destinations like Denmark, Canada, Switzerland Thailand, Russia, Iceland, France and Morocco.
According to Reuters, the U.S. State Department also raised advisories to Level 4 for locations including the French West Indies, the Marshall Islands, Ireland, Kazakhstan, Greece and Curacao.
These updates come as the U.S. said in late July that it would keep existing COVID-19 restrictions on international travel in place for now due to the COVID-19 delta variant.
"Driven by the delta variant, cases are rising here at home, particularly among those who are unvaccinated, and appears likely to continue in the weeks ahead," White House press secretary Jen Psaki said at the time, shortly after the CDC and State Department set the United Kingdom as a Level 4 risk country.
The delta variant, first detected in India, has been identified around the world and U.S. health officials said the variant accounts for an estimated 83% of the nation's coronavirus cases.
The Associated Press contributed to this report.