Robert Levinson is the longest-held American hostage in Iran. His family is now calling on the U.S. to do more to secure his release. Levinson's family said in a statement on Saturday that they're disappointed the U.S. has been unable to bring him home.

Robert Levinson, a former FBI agent, vanished in 2007. The FBI believes he was captured on Iran's Kish Island while on a mission for the CIA.

"We have been fighting for 12 and a half years to get my father home to us we know the Iranian regime is responsible for kidnapping him," Robert's daughter, Sarah Levinson Moriarty, told CBS News' Jeff Pegues. "We have no doubt whatsoever."

A photo from April 2011 showing Levinson in an orange jumpsuit still gives his family hope that eight years later he fighting and staying strong.

Last month, the Iranian government admitted in a United Nations filing that Levinson's case was "ongoing." Moriarty saw that as a ray of hope.

"It shows exactly what we've believed all along, which is that the Iranians took him back in March of 2007 and that they have the ability to send him home to us," she said.

The reward for information leading to the 71-year-old's return now stands at $25 million. Moriarity believes the reward and President Trump's Twitter messages demonstrate that the U.S. government is engaged on the issue.

"We want to know what charges they have against him," Moriarity said. "He has seven kids, he has a loving wife who is his soul mate. And he has nine grandchildren, eight of whom he hasn't met yet, so we want him home.

In October, Robert O'Brien became the president's National Security Adviser. When he worked in the State Department, he led diplomatic efforts on hostage-related matters and worked closely with the Levinson family. The family sees this as further evidence that the White House is working to bring their loved one home.