WASHINGTON - Secretary of State John Kerry said the United States has not abandoned a former FBI agent who disappeared in Iran six years ago and that he personally has raised the issue, according to an interview with ABC News.

Robert Levinson, a private detective and ex-federal agent, disappeared during a trip to an Iranian island in 2007. The White House says he was not a government employee at the time.

His lawyer, David McGee, told Reuters on Friday Levinson was investigating allegations of corruption by well-connected people in Iran. Levinson's family believes the US government has "not acted to its full capacities" in trying to free him, he said.

"There hasn't been progress in the sense that we don't have him back. But to suggest that we have abandoned him or anybody has abandoned him is simply incorrect and not helpful," Kerry said, according to excerpts from ABC television's "This Week."

"The fact is, that I have personally raised the issue not only at the highest level that I have been involved with, but also through other intermediaries," he said in the interview to be broadcast on Sunday.

Multiple news outlets reported that Levinson was in fact working for a rogue CIA operation when he disappeared. Kerry rejected that claim, according to ABC.

The top US diplomat met with Levinson's family on March 8, the day before the sixth anniversary of Levinson's disappearance. Last year, the FBI offered a rare $1 million reward for information that could lead to his safe return.

Iran has said it does not know where Levinson is, but Kerry told ABC he thinks the Iranian government can help find him.

"We're looking for proof of life," Kerry said. "There are a number of different channels that are being worked aggressively."

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