The mystery surrounding the disappearance nearly five years ago of a former Federal Bureau of Investigation agent in Iran was rekindled Friday with the release of a hostage videotape showing him alive as of a year ago.

In the video, the former agent, Robert A. Levinson, is shown in a makeshift cell looking gaunt and wearing a threadbare shirt. Mr. Levinson, who worked as a private investigator after retiring from the F.B.I., disappeared in March 2007 while on Kish Island, a resort in the Persian Gulf.

In the tape, which was received by Mr. Levinson’s family last November, he says that he has been held in captivity for three and a half years but does not identify his captors. The tape was the first sign he was still alive.

“I need the help of the United States government to answer the requests of the group that has held me,” he said on the tape as faint music played on a soundtrack. “Please help me get home. Thirty-three years of service to the United States deserves something.”