The United States has quietly begun to whittle down the population of detainees it holds at a military prison in Afghanistan, but it is struggling over what to do with less than a dozen of these non-Afghan nationals who are regarded as particularly dangerous, U.S. officials said.

This small group of foreign detainees has vexed U.S. officials for years, but the issue has become more and more pressing as a full U.S. combat withdrawal from Afghanistan looms.

The Afghan authorities have said they will not continue to hold any foreign detainees. The inmates’ home countries either do not want them or cannot provide security guarantees about their future behavior that satisfy the United States. And bringing some of them to the United States for trial in a military commission, an option being considered by the Obama administration, could run into political opposition or may be stymied by a lack of court-ready evidence.

“Where you send these people is a big problem for the U.S.,” said Jonathan Horowitz, a former State Department official who handled detainee issues in Afghanistan and is now with the Open Society Justice Initiative.

Two detainees from Saudi Arabia were repatriated this month. In November, a Palestinian was sent to a country in the Middle East that officials did not identify. Two other detainees, thought to be Pakistani, were recently determined to be Afghans and turned over to President Hamid Karzai’s government, the officials said.

The transfers bring the number of foreign detainees at the Parwan Detention Facility near Bagram air base to 49, down from 54 in November.

No easy options

U.S. officials expect to continue repatriating or resettling detainees, but they said there are no easy options for a subset of inmates suspected of serious war crimes or regarded as a continuing terrorist threat.

The Justice Department and the Pentagon were supposed to make recommendations this month on which detainees to prosecute. Officials said the number of people being looked at for prosecution is in the single digits.

Among the best candidates, officials say, is a Russian who was captured several years ago. He is suspected of participating in insurgent attacks in Afghanistan in 2009. Officials say Brig. Gen. Mark Martins, the chief military prosecutor, is eager to prosecute the Russian, whose nom de guerre is Irek Hamidullan.

The naval brig in Charleston, S.C., or a recently constructed one in Chesapeake, Va., are possible locations for any trials, said a defense official who, like others, spoke on the condition of anonymity to discuss internal deliberations.

Officials said most Bagram detainees were captured on the battle­field, making them potentially more suitable for military tribunals than trials in federal court.

Congress hasn’t placed any restrictions on the Obama administration moving detainees held in Afghanistan to the United States, as it did with those at the military detention center at Guantanamo Bay, Cuba.

Sen. Saxby Chambliss (Ga.), the ranking Republican on the Senate Select Committee on Intelligence, said in a statement: “I continue to advocate for the use of Guantanamo Bay as the logical detention location of jihadists who are captured on the battlefield. They should be tried by military commissions at GTMO, and if convicted should be dealt with on a case-by-case basis with the serious offenders kept at GTMO.”

Chambliss didn’t say whether he would block an effort to bring any of the Bagram detainees to the United States.

Sen. Lindsey O. Graham (R-S.C.) said in an interview that he would support an effort to bring Bagram detainees to the United States to face a military commission. Congress needs to be flexible, he said.

“I would be open-minded to using military commissions within the U.S.,” Graham said. “You’d have to convince me the candidate for trial was a good one and the place you’re picking is secure and what do you do if there’s a conviction. Where are you going to house the person? I don’t mind creating an alternative venue to Gitmo.”

Graham said he hasn’t ruled out Charleston, in his home state, as a possible venue.

Repatriation concerns

Among those being held at Bagram are detainees from a range of countries, including Yemen, Tunisia, Uzbekistan, Jordan and Kuwait. There are also about 35 Pakistanis, most of whom are expected to be repatriated.

The latest releases from Bagram, the two Saudis, were in their 20s when they were detained by U.S. forces in 2008. One was picked up by Afghan forces while riding in a car with several Afghans. When the Afghans realized he spoke Arabic, they turned him over to the Americans, who eventually informed the Saudi government. The second detainee said he came to Afghanistan to do volunteer work. The Saudi government was not informed of his detention until last year.

The two men were flown out of Bagram on Feb. 1, U.S. officials said. Saudi Arabia, whose rehabilitation program for militants has been praised by some U.S. officials, has consistently asked for the return of its nationals held at Guantanamo Bay and at Bagram. Most returned detainees are allowed to spent several weeks being reintegrated with their families before being put through a legal process and into the rehabilitation program.

The men are often provided the opportunity to study or given a stipend to start a business. The Saudis say all returned detainees are carefully monitored to ensure that they pose no ongoing threat.

Few other countries offer that kind of program, and repatriation could represent a grave threat for some detainees.

“No one should be returned to a place where they might face torture,” Horowitz said. “Also, the U.S. is going to have concerns if the home government is not willing or capable of maintaining law and order. Part of the solution may be for the U.S. to readjust how it weighs the purported security benefits of staying in the detention business with the political and military benefits of getting out of the detention business.”

Julie Tate and Karen DeYoung contributed to this report.