The fate of three U.S. citizens who have disappeared or been imprisoned in Iran was discussed during Friday's historic conversation between the two nations' presidents, a senior U.S. administration official said. 

U.S. President Barack Obama, during his phone call with Iranian President Hassan Rouhani, "noted our concern about three American citizens who have been held within Iran -- Robert Levinson, Saeed Abedini, and Amir Hekmati -- and noted our interest in seeing those Americans reunited with their families," the official said. 

Two of the Americans have been tried and convicted in Iranian courts, and the whereabouts of another have been unknown for more than six years. 

Here are the most recent developments in the stories of the detained U.S. citizens: 

Bob LevinsonThe family of Levinson, a retired FBI agent, has been anxiously waiting for news, any news, about his fate since he vanished during a business trip to Iran in March 2007. 

When Rouhani, Iran's new president, arrived in New York, Levinson's wife and children were watching closely for a sign that efforts to find Levinson might move forward. 

During an exclusive interview with CNN's Christiane Amanpour, Rouhani offered little when asked what he can tell Levinson's family. 

"We don't know where he is, who he is," Rouhani said. "He is an American who has disappeared. We have no news of him." 

Yet, like former President Mahmoud Ahmadinejad, Rouhani spoke of cooperation. 

"We are willing to help, and all the intelligence services in the region can come together to gather information about him to find his whereabouts," Rouhani told Amanpour. 
Where is the other one?
unknown