COVID-19-related travel restrictions were lifted at four U.S. military installations this week, allowing unrestricted travel to 90 percent of all installations.

A Defense Department statement on Tuesday noted that of 230 military installations worldwide, restrictions remain at only 24.

Eight are located in the United States, seven are in Japan and two each are in Italy, Guam and Germany. The Guantanamo Bay, Cuba, detention camp is also on the restricted list.

"Unrestricted travel is allowed for Service members or civilians between installations that have met the criteria of the Secretary of Defense memorandum on the conditions-based approach to personnel movement and travel dated March 15, 2021," Tuesday's statement says.

The Pentagon cited guidance that includes removal of local travel restrictions, availability of essential services, quality control assurance for packing and moving, and favorable health protection conditions as explanations for the new changes.

The order comes as reports of COVID-19 cases in the Department of Defense have recently declined and the availability of vaccinations, in both the military and civilian sectors, has increased.

This week the U.S. Navy announced that sailors who have been vaccinated against COVID-19 will no longer be obligated to self-isolate prior to deployment.

Those who have not been vaccinated must conduct a 14-day restriction of movement sequester, where they test in and test out prior to deployment, a protocol the Navy instituted last spring.