In the wake of reports that Pakistan has lifted restrictions on A Q Khan, US on Tuesday said that the disgraced nuclear scientists remains a "proliferation risk" and that it has taken up the issue with Islamabad.
"A Q Khan remains a proliferation risk. United States is concerned about the developments and we are following the situation," State Department Spokesman Ian Kelly said.
He said US has taken up the issue of Khan's restrictions being lifted with Pakistan.
Foreign news agencies quoted the nuclear scientist as saying that Pakistani authorities have lifted restrictions on his movements.
In February, a Pakistani court declared Khan a free man, five years after he was put under house arrest for operating a proliferation network.
The 72-year-old Khan had last week complained to a high court that his movements were still being restricted by the government's security arrangements on his behalf.