This undated handout photo provided by the family of Robert Levinson, shows retired-FBI agent Robert Levinson who went missing on the Iranian island of Kish in March 2007 and Levinson's family received these photographs of him in April 2011. (AP Photo/Levinson Family) (Uncredited/AP)

Dan Levinson is the eldest son of Robert and Christine Levinson. Their family runs the Web site

On Tuesday, my father, Robert Levinson, becomes the longest-held hostage in U.S. history. Sadly, his 6 years 8 months in captivity surpasses the 2,454 days that Terry Anderson, the former Associated Press bureau chief in Beirut, was held from his family.

My father was last seen March 9, 2007, on Kish Island, Iran, but he is not a missing person. Our family received a hostage video three years ago and photographs in 2011. In the video — in which he appears frail and visibly thinner than the 220 pounds he weighed when he was taken — my dad pleads for the U.S. government to help secure his release. In the photos, which were e-mailed to us, he is shackled. He has an unkempt beard and holds cryptic messages, the intended meaning of which we still do not understand.

What we do understand is that the Iranian government takes great pride in its security efforts. We respectfully request that the Rouhani administration help us find my father.

Our family was given hope with Hassan Rouhani’s election as Iran’s president and Javad Zarif’s appointment as foreign minister. We believe that Rouhani and Zarif, who was Iran’s ambassador to the United Nations when my father was taken, are well-respected men committed to the goodwill of all human beings, regardless of their nationality. We were heartened in September when Rouhani told CNN: “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. And we’re willing to cooperate on that.”

It’s not possible to overstate the nightmare that the past 6 years 8 months have been since my father, a retired FBI agent, disappeared while on a private business trip. My mother, four sisters, two brothers and I have tried to continue with our lives, but the situation weighs on us every day. My father has missed so many ordinary things, but he has also missed many family milestones, most recently the birth of my nephew last month. My father has missed every day of my niece’s life, and she is nearly 5. He has missed all but five months of his first grandson’s life. Another grandson is expected in February.

This is not how it was supposed to be. My father is 65, my mother 63. These are the years when my parents were supposed to be enjoying the fruits of their labor. They should be taking vacations and visiting their grandchildren. Instead, my mother is constantly on the phone with U.S. officials and pleading with the Iranian government to help us.

Two months ago, President Obama and President Rouhani spoke by phone — the first contact between the two countries’ leaders in 34 years. During the call, Obama mentioned his concern regarding my father’s situation and the importance of seeing him returned to our family. We are grateful for Obama’s efforts and hope that Rouhani will follow up on his request.

Given the negotiations between the United States and Iran over Tehran’s nuclear program, we particularly hope that officials can use their ongoing contact to resolve my father’s case. Doing so would show the world that our two countries can work together to resolve our differences and would demonstrate Iran’s willingness to help an average American family’s plight.

Read more on this issue:

Dan Levinson: Missing a father in Iran