TOKYO (Reuters) - The United States said on Saturday it will send aircraft to Japan to bring back American passengers on the quarantined cruise ship Diamond Princess, where the most coronavirus infections outside China have occurred.

The U.S. Embassy in Tokyo said in a letter on Saturday to passengers that chartered aircraft would arrive in Japan on Sunday evening and that it recommended “out of an abundance of caution” that U.S. citizens disembark and return home for further monitoring.

The U.S. Centers for Disease Control and Prevention (CDC) said there are approximately 400 U.S. citizens onboard the Diamond Princess.

The passengers will be required to undergo further quarantine of 14 days upon arriving in the United States and if they choose not to return on the aircraft, they would not be able to return home “for a period of time,” the letter said.

“We understand this is frustrating and an adjustment, but these measures are consistent with the careful policies we have instituted to limit the potential spread of the disease,” it said.

In a statement, the CDC said all of the travelers from Japan will be screened before boarding the State Department-chartered aircraft “to prevent symptomatic travelers from departing Japan.”

“The passengers will be screened before leaving the ship and monitored and evaluated by medical and public health personnel every step of the way, including before takeoff, during the flight and after arrival,” the CDC said.

FILE PHOTO: A passenger wearing a mask stands on the deck of the cruise ship Diamond Princess, as the vessel's passengers continue to be tested for coronavirus, at Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan February 13, 2020. REUTERS/Kim Kyung-Hoon/File Photo

The passengers will undergo temperature checks and observation for respiratory symptoms, the CDC added.

The Embassy said the U.S. government was working with Japan so that any people with symptoms would receive proper care if they could not board the aircraft.

Japan confirmed it was coordinating with the U.S. government for Americans to leave the ship and return home, saying that would ease its burden in resolving the situation.

Other countries might follow suit and ask to bring back their own citizens from the ship before the quarantine period ends next week, a Japanese government official told reporters.

The cruise ship, owned by Carnival Corp CCL.N, has been quarantined since arriving in Yokohama on Feb. 3, after a man who disembarked in Hong Kong before it traveled to Japan was diagnosed with the virus.

It had some 3,700 passengers and crew on board. Another 67 people have tested positive for the virus, Japanese Health Minister Katsunobu Kato said on Saturday, bringing the total to 285 cases. Those testing positive are transferred to Japanese hospitals.

The cruise liner’s quarantine is set to end on Wednesday and while some passengers were disheartened at the prospect of more time in quarantine, others were more understanding.

“They are very concerned about spreading the virus, and there’s no good way to transport people from Japan without possible transfer of virus, so it is the logical thing to do,” Sawyer Smith, 25, told Reuters.

The U.S. aircraft will land at Travis Air Force Base in California and some passengers will then continue onward to Lackland Air Force Base in Texas. The passengers will be housed at those bases during the quarantine period, the CDC said, and will be kept separate from people already in quarantine from previous repatriation flights from the Chinese city of Wuhan, the epicenter of the outbreak.

In a statement, the Pentagon said it has extended through March 15 the availability of four military installations as temporary housing facilities related to the coronavirus including Travis, Lackland, Fort Carson in Colorado and Marine Corps Air Station-Miramar in California.

The Embassy letter did not specify how long U.S. citizens who choose not to board the chartered aircraft might have to wait before they could return home, saying only that the final decision would be up to the CDC.