The United States is offering a rare $1 million reward for information leading to the safe return of a former Federal Bureau of Investigation agent who vanished in Iran five years ago and is believed to be held hostage in the area.

The FBI announced the reward Tuesday, its latest high-profile effort to determine the whereabouts of retired special agent Robert Levinson.

Levinson vanished from Iran's Kish Island in 2007 while on a business trip. Friday marks the fifth anniversary of his disappearance.

Late last year, a short video of Levinson was released by his family, generating enormous publicity but no concrete leads. The private investigator looked gaunt and appealed for help because he was “running very quickly out of diabetes medicine.” The family had received the video in 2010, but it was held for release because federal officials thought it would complicate their investigation.

The $1 million reward is rare in kidnapping cases and is being funded by the U.S. Justice Department. The U.S. still has not identified Levinson's abductors, but there are indications he is being held along the borders of Afghanistan, Iran and Pakistan.