Khost, Afghanistan - A US soldier is believed to have been captured by insurgents in Afghanistan, the military said Thursday, as a commander for a hardline Taliban faction said his militia had the trooper.

    It was believed to be the first time militants had abducted an American soldier in Afghanistan since US troops were deployed to oust the Taliban regime in 2001 and then remained to fight a growing extremist insurgency.

    "A US soldier who has been missing since June 30 from his assigned unit is believed to have been captured by militant forces," US military spokeswoman Captain Elizabeth Mathias told AFP.

    She said it was the first time an American soldier had been captured in two to three years in Iraq or Afghanistan.

    Mathias could not confirm it was the first such case for this country although other officials said they believed it was.

    "We are using all of our available resources to find him and provide for his safe return. We are not providing further details to protect the soldier's situation and well-being," she said.

    A commander of the Taliban's hardline Haqqani faction told an AFP reporter that his militia had captured a US trooper and three Afghans in the province of Paktika, which borders Pakistan.

    "One of our commanders named Mawlawi Sangin has captured a coalition soldier along with his three Afghan guards in Yousuf Khail district of Paktika province," the commander, named only Bahram, told AFP.

    "The coalition soldier has been taken to a safe place," he said.

    The militia's leaders would likely issue demands for his release, said the commander who is known to the reporter.

    "Our leaders have not decided on the fate of this soldier. They will decide on his fate and soon we will present video tapes of the coalition soldier and our demand to media," he said.

    A spokesman for the top US commander General Stanley McChrystal said the soldier was captured outside his base camp.

    "It was not that the insurgents came into base and it was overrun ... he left the base camp. At some point he was taken by insurgents," Rear Admiral Greg Smith told AFP.

    "We have high confidence that he is in the hands of insurgents."

    The soldier was only reported missing after he failed to come on duty on June 30 and was not found after a search, Smith said.

    The US military has described the Al-Qaeda-linked Haqqani network as one of the "most lethal Taliban organisations".

    In recent months the military has launched several attacks on the group, which it says operates out of Pakistan's Federally Administered Tribal Area just across the border.

    The network is said to be behind several attacks in Kabul, including one on a five-star hotel in 2008 and the attempted assassination of President Hamid Karzai in April last year.

    The capture of the soldier comes as nearly 4,000 newly deployed US Marines launched a major operation in the province of Helmand Thursday, pushing south to take control of Taliban strongholds ahead of August 20 elections.

    Taliban and other insurgents have been behind several kidnappings in Afghanistan and have killed some of their hostages, including foreign nationals.

    There are around 56,000 US soldiers operating in Afghanistan, according to Pentagon figures, in the biggest deployment from one country helping to fight an insurgency led by the Taliban who were in government between 1996 and 2001.