The Taliban''s new top operations officer in southern Afghanistan had been a prisoner at the Guantanamo Bay detention center, the latest example of a freed detainee who took a militant leadership role and a potential complication for the Obama administration''s efforts to close the prison. U.S. authorities handed over the detainee to the Afghan government, which in turn released him, according to Pentagon and CIA officials.

Abdullah Ghulam Rasoul, formerly Guantanamo prisoner No. 008, was among 13 Afghan prisoners released to the Afghan government in December 2007. Rasoul is now known as Mullah Abdullah Zakir, a nom de guerre that Pentagon and intelligence officials say is used by a Taliban leader who is in charge of operations against U.S. and Afghan forces in southern Afghanistan.

The officials, who spoke anonymously because they are not authorized to release the information, said Rasoul has joined a growing faction of former Guantanamo prisoners who have rejoined militant groups and taken action against U.S. interests. Pentagon officials have said that as many as 60 former detainees have resurfaced on foreign battlefields.

Pentagon and intelligence officials said Rasoul has emerged as a key militant figure in southern Afghanistan, where violence has been spiking in the last year. Thousands of U.S. troops are preparing to deploy there to fight resurgent Taliban forces.

One intelligence official told the Associated Press that Rasoul''s stated mission is to counter the U.S. troop surge.