The family of a former FBI agent who vanished in Iran in 2007 has released a hostage video showing him alive and asking for help.

The video shows Robert Levinson, looking gaunt, asking for the U.S. government's help to answer the requests of the group that has held me for 3-1/2 years, but he does not identify the captors.

Levinson's son and wife on Friday posted a video message asking the captors to tell them their demands to gain Levinson's release.

In March, U.S. Secretary of State Hillary Clinton said the United States had seen indications that Levinson was being held in southwest Asia, and appealed to Iran to provide information about him.

The State Department said on Friday the FBI had lead responsibility for the case, and expressed hope that release of the video would spur new leads.

We have been sharing relevant information that we have about this case with many governments to see what we can do, State Department spokeswoman Victoria Nuland told a news briefing.

Obviously we're all hopeful that this will bring more leads.

Washington cut diplomatic relations with Tehran shortly after Iran's 1979 Islamic revolution and the two countries have been increasingly at odds over a range of issues. Iran's military on Sunday said it had shot down a U.S. reconnaissance drone in eastern Iran, heightening tensions.

Levinson in the video said he was being treated well but that, I am not in very good health. I am running very quickly out of diabetes medicine.

In the family's response, one of Levinson's son, David, said the video was a comfort to the family because it shows us that my father is alive and that he looks healthy.

My mother has received your messages, he says. Please tell us your demands so we can work together to bring my father home safely. Thank you for taking care of my father and for continuing to provide him with the care and medical treatment he needs to stay alive.

Levinson disappeared while on a business trip to Iran's Kish island.

(Reporting by Vicki Allen; additional reporting by Andrew Quinn, Editing by Jackie Frank)