WASHINGTON (AP) — The FBI has increased the reward for information leading to the return of a former FBI agent who went missing eight years ago from the Iranian resort of Kish Island.

In a statement Monday, the FBI said the U.S. government will pay up to $5 million for information that can help bring Robert Levinson home, up from $1 million.

FBI Director James Comey said "it is long past time for Bob to come home." Secretary of State John Kerry urged the Iranian government to "work cooperatively with us on the investigation."

An Associated Press investigation published in 2013 revealed that Levinson vanished while working for the CIA on an unapproved intelligence-gathering mission.

Tuesday is Levinson's 67th birthday. He retired from the FBI in 1998.