July 2: A U.S. Marine takes up a fighting position after off loading from a helicopter during the start of Operation Khanjar.
Insurgents have captured an American soldier in eastern Afghanistan after he walked off post with his three Afghan counterparts, officials said Thursday.
Spokeswoman Capt. Elizabeth Mathias said the soldier disappeared Tuesday. The U.S. military is offering a $25,000 reward to any Afghan national for information about the soldier's whereabouts.
"We have all available resources out there looking for him and hopefully providing for his safe return," Mathias said.
There are indications that the soldier who was captured was "disaffected" and that he left the base to meet up with several Afghan nationals who were members of the security forces that he had been working with to train, one U.S. defense official tells FOX News.
"He was not of sound mind when he did what he did. Not smart," the official said.
The soldier was handed over to the Haqqani network, a group with ties to the Taliban, and the same group that captured New York Times correspondent David Rhode.
U.S. officials believe the soldier is still being held in Afghanistan - and has not crossed into Pakistan's Waziristan province.
Maulvi Sangin, who claims to speak for the Taliban in the province, said that the U.S. soldier was seized when he and the others were on their way to the Yousafkhel security checkpost, and took them to a secret location, according to an Afghan news Web site obtained by MEMRI, The Middle East Media Research Institute. Sangin claimed the abducted soldiers were drunk when captured by the Taliban.
U.S. officials could not confirm that these claims are true, and not Taliban propaganda.
The news broke as thousands of U.S. Marines launched a major anti-Taliban offensive in southern Afghanistan. The missing soldier was not part of that operation.
"We are not providing further details to protect the soldier's well-being," she said.
Afghan Police Gen. Nabi Mullakheil said the soldier disappeared in the Mullakheil area of eastern Paktika province, where there is an American base.
The soldier was noticed missing during a routine check of the unit on Tuesday and was first listed as "duty status whereabouts unknown," a U.S. defense official said on condition of anonymity.
It wasn't until Thursday that officials said publicly that he was missing and described him as "believed captured." Details of such incidents are routinely held very tightly by the military as it works to retrieve a missing or captured soldier without giving away any information to captors.
Initial reports indicated that the soldier was off duty at the time he disappeared, having just completed a shift, the official said on condition of anonymity because details are still sketchy.
The missing man is an enlisted soldier, and his family has been notified.
Two U.S. defense sources said the soldier "just walked off" post with three Afghan counterparts after he finished working. They said they had no explanation for why he left the base. He was assigned to a combat outpost, one of a number of smaller bases set up by foreign forces in Afghanistan, the officials said.
Zabiullah Mujaheed, a spokesman for the Taliban, could not confirm that the soldier was with any of their forces. A myriad of insurgent groups operate in eastern Afghanistan, and the Taliban is only one of them.
The most important insurgent group operating in that area is known as Haqqani network and is led by Siraj Haqqani, whom the U.S. has accused of masterminding beheadings and homicide bombings.
The Associated Press and FOX News' Jennifer Griffin contributed to this report.