The president suggested 30,000 migrants could be housed on the base. It is unclear how the plan will take shape.

In pushing back against President-elect Donald J. Trump’s plan, President Xiomara Castro threatened that a base hosting U.S. troops could “lose all reason to exist in Honduras.”

The prisoner, who was repatriated to Tunisia, was never charged. His transfer is part of a Biden administration push to further reduce the dwindling detainee population at the wartime prison.