Suspected Taliban (search) gunmen kidnapped and hanged a pro-government tribal leader in southern Afghanistan, an official said Saturday, describing the latest killing of an ally of President Hamid Karzai (search).

Agha Jan (search) was kidnapped Thursday with his two sons, brother and two nephews from his home in southern Zabul province, said local police chief Gul Habib Jan. Agha Jan's relatives were freed unharmed, but the tribal chief's body was found Friday.

"He was a strong supporter of President Hamid Karzai's government and he was against the Taliban movement," the police chief said.

Dozens of prominent supporters of Karzai's U.S.-backed administration, along with more than 700 others, have been killed during an upsurge in violence since March. U.S. and Afghan officials have warned that the violence likely will worsen before legislative elections set for September.

On Friday, suspected Taliban fighters raided a police post in the country's south, and the ensuing shootout left seven officers and five attackers dead.

Meanwhile, the U.S. military Saturday released 20 Afghans from detention after they were determined to no longer represent a threat, U.S. military spokeswoman Sgt. Marina Evans said.

A total of 133 detainees have been released from Bagram, the main American base in Afghanistan, an hour's drive north of the capital, Kabul, over the past two weeks. Another 46 are to be released shortly, Evans said.

The releases came as U.S. and Afghan forces continued to search for four suspected Arab terrorists who escaped from the fortress-like prison Monday.

Some of the released prisoners said they were amazed to hear of the jailbreak.

"I can't imagine how those four escaped. It is not possible to escape from Bagram," said Zain Nuddin, who is from southern Kandahar province and was detained for 11 months after being suspected of having links to Afghanistan's ousted hard-line Taliban movement.

"Every three days, we are only allowed out to exercise for 25 minutes and there are always so many American soldiers with guns watching us."