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The US has been secretly releasing captured Taliban fighters from a detention center in Afghanistan in a bid to strengthen its hand in peace talks with the insurgent group, the Washington Post reported Monday.

The "strategic release" program of high-level detainees is designed to give the US a bargaining chip in some areas of Afghanistan where international forces struggle to exercise control, the report said.

Under the risky program, the hardened fighters must promise to give up violence and are threatened with further punishment, but there is nothing to stop them resuming attacks against Afghan and American troops.

"Everyone agrees they are guilty of what they have done and should remain in detention. Everyone agrees that these are bad guys. But the benefits outweigh the risks," a US official told the Post.

In a visit to Afghanistan last week, President Barack Obama confirmed that the US was pursuing peace talks with the Taliban.

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"We have made it clear that they [the Taliban] can be a part of this future if they break with Al Qaeda, renounce violence, and abide by Afghan laws. Many members of the Taliban -- from foot soldiers to leaders -- have indicated an interest in reconciliation. A path to peace is now set before them," Obama said.

A stumbling block in the US-Taliban peace talks has been the US refusal to approve the transfer of five Taliban detainees from Guantanamo Bay to Qatar, which the Taliban says is necessary for negotiations to proceed.

The clock is ticking also on the US handover of security control to the Afghans.

At the upcoming NATO summit in Chicago, the US coalition will set a goal for Afghan forces to take the lead in combat operations across the country next year.

During his short visit, Obama and Afghan President Hamid Karzai signed a partnership deal that charts a 10-year relationship between the US and Afghanistan once the majority of American and foreign forces pull out of the country in 2014.