The US Federal Bureau of Investigation is offering one million dollars for information leading to the safe return of one of its former special agents.

Bob Levinson has not been seen in public since he travelled to Iran in 2007.

It's thought he's being held hostage in the border region of Iran, Pakistan and Afghanistan.

Levinson's wife Christine joined FBI top brass on Tuesday to remember the husband she hasn't seen for five years.

On the steps of the Bureau's Washington DC Field Office, she said: "There are no words to describe the nightmare my family and I have been living everyday.  I never imagined that we would still be waiting for Bob to come home five years later."

The small gathering of FBI staff was joined by the organisation's current director Robert Mueller - the guy putting up the one million.

Part of the 'family'

Muellter told Mrs Levinson and her friends and family: "We in the FBI are working everyday to bring your husband, your father and your grandfather back home to you."

The FBI says a million dollars is a lot of money but they've had success with this type of reward in the past, and though Levinson was a retired offer, he's still part of the "family" and it wants him back.

In a video posted on the website helpboblevinson.com, Levinson, who served 28 years in law enforcement [22 at the FBI], can be seen saying telling his captors' camera that he's in poor health.

He was working as a private investigator when he went missing on a trip to Iran's Kish Island in 2007.

It's thought he was looking into tobacco smuggling.

A new set of photographs has been released showing how Levinson may have aged during five years captivity.

The FBI's launching a publicity campaign in Southwest Asia to highlight Levinson's plight.

For his wife Christine, concrete news of her husband can't come soon enough.  She was almost in tears as she read out these words during Tuesday's news conference: "We hope one day soon to post the following message thank you everyone Bob is home."