Robert Levinson

"It's a very important acknowledgment, probably long overdue," a senior U.S. official tells reporters on a conference call about the sanctions. Former FBI agent Robert Levinson went missing in 2007.

Robert Levinson, who went missing while on an unauthorized mission for the CIA, is thought to have died in Iranian custody, his family says.

Those detained include a former Marine, a pastor and a Washington Post reporter. The missing man is a former FBI agent. The U.S. says Iran should "make a humanitarian gesture and bring" them home.