However, United Nations officials have yet to lift their own international travel bans on four of them, so the only place they could legally travel to is their home country, Afghanistan, where government officials have made it clear they would promptly be taken into custody.

Image Sgt. Bowe Bergdahl Credit... U.S. Army

A second senior American official in Washington said last week that Qatari officials were eager to see the five men leave their country. The only possible route for them to take would be to Pakistan, which would cause a political problem between Afghanistan and Pakistan, which lately have sought to mend relations.

In addition to American concerns, Afghan officials have also expressed unease about the possibility of the former prisoners returning to fight.

“It would be a matter of great concern if they return to the battlefield,” said a senior security official in Kabul on Sunday. “We have seen that in the past, that Taliban members who were freed returned to the battlefield. Their unconditional freedom can add fuel to the fire and can boost Taliban morale.”

Underscoring the concern in the United States about the former detainees is the view that the trade was an unequal one: Four are depicted in reports by the United Nations sanctions committee and by American military interrogators as major figures with blood on their hands.

The five include a one-time Taliban spokesman, Khirullah Said Wali Khairkhwa, who was also a minister of internal affairs in the Taliban government, and was implicated in the massacre of Shiite civilians. Mullah Mohammad Fazl, a former deputy army chief of staff for the Taliban, was accused of carrying out massacres of Hazara civilians, and was also described as one of the founders of the Taliban, along with Mullah Omar.

An American military interrogator said Mullah Fazl justified the killings as a wartime necessity, and also dismissed the killings of Iranian diplomats in Herat on the grounds that they were foreigners and supported the enemy. Mullah Norullah Noori was a former provincial governor accused of responsibility in the killing of thousands of Shiites during the Taliban rule. Abdul Haq Wasiq was the former deputy intelligence director under Mullah Omar. Those four are all under United Nations sanctions, including a travel ban, and the complex procedure of lifting such a ban has not yet been started by the Security Council because no member country has made the request needed to do so.