This is a dispatch from the reporters' "pool," a Pentagon-authorized system that allows a single journalist to file for all accredited news organizations.

GUANTANAMO BAY NAVAL STATION, Cuba — Al Qaeda and Taliban prisoners were allowed an exercise walk Saturday — with their hands bound and a U.S. soldier on each side — and given medical exams on their first full day under tight security at this remote U.S. military outpost, U.S. officials said.

The head of security at Camp X-Ray, the base's detention area, said he was confident in the "layered" security measures, with backup guards in place for the 20 prisoners, considered some of the toughest of the fighters captured in Afghanistan.

"This was sort of our test run. It went extremely well," Army Col. Terry Carrico told reporters. "There's going to be no break out. I'm very confident."

The 20 are the first of hundreds of Al Qaeda and Taliban prisoners expected to be brought from Afghanistan to Guantanamo Bay, on the eastern tip of Cuba. Here they will face intense interrogation, especially concerning the whereabouts of terror suspect Usama bin Laden. Officials have not said when the next group of prisoners will be brought here.

The prisoners' identities have not been released. The British Foreign Office said it had been informed by the Americans that a British citizen was among the 20 prisoners. British officials were trying to determine who he is.

The U.S. military has clamped down with heavy security, saying the fighters have shown they're willing to kill themselves and their captors. In November, a prison mutiny in northern Afghanistan took three days to put down, left as many as 450 fighters dead and cost the life of a CIA agent.

The captives were being detained outside the view of reporters in a camp behind coils of barbed wire, guarded by heavily armed military police.

After their arrival Friday afternoon, the group's first night in Cuba "was peaceful," Carrico said.

There was some conversation among prisoners, and he said he saw several put their "mats down on the deck and pray" before going to sleep. "They were very fatigued."

They slept under the glare of halogen floodlights in individual outdoor cells made of chain-link fence — measures aimed at keeping them visible to their guards. It rained overnight, but the prisoners were sheltered by their cells' metal roofs, Carrico said.

On Saturday, the prisoners were to be given meals and showers, and be allowed to walk around outside their cells. But during the exercise walk, each was to have his hands bound and a military police guard at each side, Carrico said.

Camp medics were also examining the prisoners. Carrico said some arrived wearing surgical masks after initial tests suggested the presence of tuberculosis. Those prisoners were to undergo chest X-rays to confirm whether they were infected, he said.

Each prisoner will be given a Quran as a "comfort item" if he doesn't have one, Carrico said. Each also receives two bath towels — one for a prayer mat and the other for showering — a washcloth, toothpaste, toothbrush, soap and shampoo.

An Air Force C-141 cargo plane touched down with the prisoners Friday afternoon. The shackled men were led off the plane and into buses by more than 50 Marines. Several detainees appeared to struggle with the Marines, and two were forced to their knees on the tarmac before being allowed to stand again and walk to the buses. At least one prisoner had been sedated on the flight from Afghanistan.

The buses took the men to a ferry, which carried them across Guantanamo Bay to Camp X-Ray.

The camp has room for 100 prisoners now and soon could house 220. A more permanent site under construction is expected to house up to 2,000.

The Red Cross and other groups are to monitor conditions, amid worries by some human rights groups that the heavy security measures violate the prisoners' rights and that U.S. officials plan military tribunals for the prisoners with lowered standards of due process.

U.S. officials insist conditions do not violate human rights.

The United States is reserving the right to try Al Qaeda and Taliban captives on its own terms and is not calling them "prisoners of war," a designation that would invoke the Geneva Convention.

The Guantanamo base is one of America's oldest overseas outposts. The U.S. military first seized Guantanamo Bay in 1898 during the Spanish-American War.