"There are restrictions on Khan imposed by the Pakistani government," Director of National Intelligence Dennis Blair told the House Permanent Select Committee on Intelligence during an open hearing.
Responding to a question from Anna Eshood, the Democratic Congressman from California, Blair said these restrictions primarily involve insuring that Khan is not connected to the network that he used before for the proliferation activities.
"But he's not a head of a laboratory, which is in the business that he was in before," Blair said, adding details of his proliferation network could be given in a close session only.
Congresswoman Eshood said she was "shocked and appalled" when A Q Khan's release from house arrest was announced.
Khan, who was released early this month after spending four years under house arrest, has been accused of sharing nuclear know-how with countries like North Korea, Iran and Libya.
Last month, the US had slapped sanctions on Khan and those involved in his network.