The Taliban are poised to release a US Army soldier who has been held hostage since 2009 in exchange for five senior rebels imprisoned in Guantanamo Bay.

Shaheen Suhail told Associated Press that Sgt Bowe Bergdahl, the only American soldier held captive from the Afghan war, is "as far as I know, in good condition".

The offer would represent a conciliatory gesture following the official opening of a Taliban political office in the Qatari capital of Doha.

The US agreed to drop a series of preconditions to start direct talks with Taliban leaders in the hope of ending the 12-year conflict in Afghanistan.

Washington said that a formal rejection of al-Qaida by the Taliban would be a "negotiating aim" rather than a precondition for talks.

Suhail said the prisoner exchange was the first Taliban request before opening peace talks.

"First has to be the release of detainees," Sukhail said. "Yes. It would be an exchange. Then step by step, we want to build confidence to go forward.

"We want foreign troops to be pulled out of Afghanistan. If there are troops in Afghanistan then there will be a continuation of the war."

Bergdahl, from Hailey, Idaho, disappeared from his base in southeastern Afghanistan on June 2009. It is believed he has been held in Pakistan.

US Secretary of State John Kerry was due to meet with the Taliban in Doha. But the group's move to name the new office the "Political Office of the Islamic Emirate of Afghanistan" angered Afghan president Hamid Karzai, who pulled out of security talks with Washington in protest.