President Donald Trump last week ordered the preparation of a 30,000-person "migrant facility" at the base, which is primarily known as a detention center for suspects accused of terrorism-related offenses, but which also has a history of holding migrants.

"These 10 high-threat individuals are currently being housed in vacant detention facilities," the Pentagon said in a statement, referring to them as "illegal aliens."

"US Immigration and Customs Enforcement is taking this measure to ensure the safe and secure detention of these individuals until they can be transported to their country of origin or other appropriate destination," it said.

White House Press Secretary Karoline Leavitt later said the flight carrying the migrants had arrived the previous day and that they were "10 members of the transnational gang Tren de Aragua."

The Trump administration has launched what it has cast as a major effort to combat illegal migration that has also included immigration raids, arrests and deportations on military aircraft.

The president has made the issue a priority on the international stage as well, threatening Colombia with sanctions and massive tariffs for turning back two planeloads of deportees.

The Guantanamo prison was opened in the wake of the September 11, 2001 attacks and has been used to indefinitely hold detainees seized during the wars and other operations that followed.

Conditions there have prompted outcry from rights groups, and UN experts have condemned it as a site of "unparalleled notoriety."