Two vaccinated guests aboard Celebrity Millennium remained in isolation Thursday after testing positive for COVID-19, Royal Caribbean Group announced.

"The individuals are asymptomatic and currently in isolation and being monitored by our medical team," the Miami-based cruise operator said in a statement Thursday. "We are conducting contact tracing, expediting testing for all close contacts and closely monitoring the situation."

Celebrity Millennium departed from St. Maarten in the Caribbean on Saturday.

The guests tested positive while they underwent "required end-of-cruise testing," the cruise line said.

"All guests on Celebrity Millennium were required to show proof of vaccination as well as a negative COVID-19 test within 72 hours before sailing from St. Maarten this past Saturday," Royal Caribbean Group added.

Celebrity Millennium is sailing with fully vaccinated crew and guests.

The ship is following safety guidelines that exceed the Center for Disease Control and Prevention requirements, the cruise line said. The additional requirements are aimed at protecting the health and safety of guests.

"This situation demonstrates that our rigorous health and safety protocols work to protect our crew, guests and the communities we visit," the cruise line said.

The positive tests on Celebrity Millennium come as Florida continues a legal battle against the CDC to resume sailings from the Sunshine State. The fight continued Thursday in a federal courtroom in Tampa and remains unresolved. At issue is how guests sailing from Florida should prove their vaccination status.

Florida Gov. Ron DeSantis opposes so-called "vaccine passports." The state Attorney General Ashley Moody, backed by DeSantis, filed a lawsuit in April challenging CDC restrictions.

A state ban against vaccine passports takes effect July 1. Under the law, any business — including cruise lines — could face a fine of up to $5,000 for each violation.

Royal Caribbean Group recently announced it received approval to resume sailings from the United States later this month.

The Celebrity Edge is set to depart from Port Everglades in Fort Lauderdale on June 26. The ship is sailing under the Celebrity Cruises brand.

Royal Caribbean Group owns and operates three brands: Royal Caribbean International, Celebrity Cruises, and Silversea Cruises.

"All sailings will depart with vaccinated crew and everyone over the age of 16 must present proof of vaccination against COVID-19; as of August 1, 2021, all guests ages 12 and older must present proof of vaccination," Royal Caribbean Group added.