Pakistani prison authorities have moved the jailed doctor believed to have helped the CIA hunt down Osama bin Laden, his attorney said Saturday, speculating it could be a prelude to his release.

The continued imprisonment of Shakil Afridi has long been a source of tension between Pakistan and the United States, which cut military aid over accusations Pakistan continues to shelter Taliban militants fighting U.S. and Afghan soldiers across the border in Afghanistan.

A jail official in the northwestern city of Peshawar said on condition of anonymity that Afridi had been transferred to Adiala prison in Rawalpindi, near the capital Islamabad, but said the reasons were unclear and could simply be security-related.