The Level 3: Reconsider Travel Advisory says, in part:

"The Department of State advises U.S. citizens to reconsider travel abroad due to the global impact of COVID-19. Many areas throughout the world are now experiencing COVID-19 outbreaks and taking action that may limit traveler mobility, including quarantines and border restrictions. Even countries, jurisdictions, or areas where cases have not been reported may restrict travel without notice.

"On March 14, the Department of State authorized the departure from any diplomatic or consular post in the world of US personnel and family members who have been medically determined to be at higher risk of a poor outcome if exposed to COVID-19.

"If you decide to travel abroad:

• Review and follow the CDC’s guidelines for the prevention of coronavirus.
• Check with your airlines or cruise lines regarding any updated information about your travel plans and/or restrictions.
• Visit travel.state.gov to view individual Travel Advisories for the most urgent threats to safety and security.
• Visit our Embassy webpages on COVID-19 for information on conditions in each country or jurisdiction.
• Visit the Department of Homeland Security’s website on the latest travel restrictions to the U.S."

Note the mention of "quarantines and border restrictions". See the story here about European tourists stuck indefinitely in hotels in Morocco.