Abu Dhabi, United Arab Emirates (CNN) -- Seven years ago Sunday, American Bob Levinson disappeared after traveling to Iran. He's now one of the longest-held American citizens in history.
Recently, the 65-year-old's family has said publicly that he worked for the CIA. Their decision to speak out came after news stories published in 2013 said Levinson worked for the spy agency.
For years the family kept it quiet that Levinson was working for the CIA, because the United States government had warned them that revealing it would put Levinson in more jeopardy, they said.
On Saturday, Levinson's son Dan Levinson talked in person with CNN in Abu Dhabi.
"I am here in Abu Dhabi. Without getting in specifics, I think the important thing is to show that we are not giving up," he said. He told CNN he was back in the region doing all he could to find his father.
He stressed that the family wants his father to remain part of ongoing discussions between Iran and six world powers, including the U.S., over Tehran's nuclear program.
"There is a lot of opportunity in the next few months before that expires to continue discussions between the officials of our government and the Iranian government," he said. "And we think that is a prime opportunity, because these kinds of discussions have never -- have not really taken place for decades." He said Monday would be his father's 66th birthday.
The case gained renewed urgency in December, when The Associated Press and The Washington Post reported that Bob Levinson was working as an independent CIA contractor when he disappeared.
According to the news reports, Levinson had gone to Iran on a mission to investigate corruption involving Iranian officials, according to an e-mail obtained by the family. Levinson disappeared shortly after arriving at Kish Island and has not been heard from since a 2010 video.
Of the news reports that prompted the family to talk about what they say are Levinson's ties to the CIA, Dan Levinson said, "We didn't decide to come forward with it, but it did happen. If anything, we are hoping to use this and ensure that it speeds up the process of getting my dad home."
The FBI, White House and CIA have not publicly acknowledged any connection between the CIA and Levinson.
In January, Iranian Minister of Foreign Affairs Mohammad Javad Zarif told CNN, "I have not seen anything that could prove that (Levinson) was ever in Iran."
"In fact, we have seen evidence ... he was last seen alive outside Iran, with pictures showing that he was outside Iran when he was last seen. It's a very unfortunate case," Zarif said. "We've said clearly that we have no knowledge of his whereabouts. ... We need the United States to explain for Iran what a CIA operative was doing, if he was ever in Iranian territory, what was he doing in Iranian territory."
In a statement released Sunday, Secretary of State John Kerry said the U.S. "remains committed to the safe return of Mr. Levinson to his family."
"We appreciate the support and assistance from our international partners as we work to end this awful separation," Kerry said. "Given Mr. Levinson's health, age, and length of time in captivity, we mark this anniversary with a special sense of urgency."
"We respectfully ask" the Iranian government to "work cooperatively with us" on the Levinson investigation, Kerry said.
Kerry called for anyone with information about the case to contact the FBI, which is offering a $1 million reward for any information that leads to Levinson's safe return.
Levinson retired as a special agent of the FBI in 1998, the agency said in a written statement Friday. The statement said that Levinson traveled to Kish Island as a private investigator. "He went missing the next day," the statement reads.
"The FBI is responsible for investigating crimes committed against U.S. citizens abroad and has been conducting an investigation" to find Levinson, the statement says.
"Bob's absence over the past seven years has exacted an enormous toll on his family, and we will not waver in our commitment to bringing him home safely to his loved ones and his country," said FBI Director James B. Comey. "We continue to request the assistance of our international partners as well as the Islamic Republic of Iran, and we continue to ask anyone with information regarding Bob's disappearance to contact the FBI."
About 20,000 former and current FBI agents observed a moment of silence Friday to mark the anniversary of Levinson's disappearance.
For the Levinson family, the pain continues.
"Bob's continued imprisonment defies the humanity in all of us," the family said in a written statement Friday. "After seven years, we have almost no words left to describe our life without Bob. We miss his face, his voice, his laughter, his wisdom and his embrace. We miss everything about Bob. No matter where we turn, Bob is absent.
"Bob, if you are able to see or hear this message, we urge you to be strong."
CNN's Susan Candiotti contributed to this report. CNN's Brice Laine reported from Abu Dhabi and Ashley Fantz wrote this story in Atlanta.