WASHINGTON — The Defense Department said yesterday that 16 detainees from the military prison in Guantanamo Bay, Cuba, have been transferred to their home nation of Saudi Arabia in recent days, a sizable handover of “enemy combatants” that is part of the American government’s effort to empty the facility.

The detainees were transferred to the custody of the Saudi Arabian government and arrived in Riyadh yesterday, according to Pentagon officials. Approximately 75 detainees have been sent to Saudi Arabia in the past few years as part of negotiations between the two governments. There are about 50 Saudi Arabian detainees remaining at Guantanamo.

The transfer leaves about 360 foreign detainees in Guantanamo, about 80 of whom have been cleared for release or transfer, according to the American military. Military prosecutors hope to bring as many as 80 more to trial in military commissions, which are currently stalled by legal challenges to the process and a pending Supreme Court review.

“We are trying to reduce the population there,” a Pentagon spokesman, Navy Commander J. D. Gordon, said. “There are certain risks you take with every transfer, and we’re trying to ensure that detainees can be transferred back to their home countries. Today’s was a fairly large group. We’re down to 360, so we’re making progress there.”