Story highlights Secretary of State John Kerry says he's raised issue of Levinson "at the highest level"

Levinson disappeared almost 7 years ago on an alleged business trip

Multiple reports this past week suggest Levinson may have been working for the CIA

McCain: If the government lied about Levinson, it may be time to reassess oversight

The United States hasn't abandoned Robert Levinson, the retired FBI agent described by his wife as the "longest-held American hostage," Secretary of State John Kerry said Sunday.

"There hasn't been progress in the sense that we don't have him back. But to suggest that we've abandoned him or anybody ... is simply incorrect and not helpful," Kerry told ABC'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."

Levinson disappeared in Iran in March 2007 during a business trip, purportedly undertaken as a private investigator looking into cigarette smuggling. However, The Associated Press and the Washington Post reported Thursday that contrary to what the State Department and Levinson's family have said for years, Levinson actually was working for the CIA in Iran. And a source involved in the matter told CNN there's proof that Levinson worked for the CIA undercover, and under contract, while also working as a private investigator.

That allegation doesn't sit well with Sen. John McCain, R-Arizona, who is on the Senate Committee on Foreign Relations.

JUST WATCHED Fmr. CIA officer: Levinson likely alive Replay More Videos ... MUST WATCH Fmr. CIA officer: Levinson likely alive 05:01

"What disturbs me is apparently they did not tell the truth to the Congress. The CIA did not tell the truth to the American Congress about Mr. Levinson," McCain said Sunday on CNN's "State of the Union." "If that's true, then you put this on top of things that our intelligence committees didn't know about other activities, which have been revealed by (NSA leaker Edward) Snowden -- maybe it means that we should be examining the oversight role of Congress over our different intelligence agencies."

Iran's government repeatedly has said it is not holding Levinson and does not know his whereabouts. During a September interview with CNN's Christiane Amanpour, Iranian President Hassan Rouhani was asked what he could tell Levinson's family.

"We don't know where he is, who he is," Rouhani said. "He is an American who has disappeared. We have no news of him."

Kerry said the United States is still looking for proof that Levinson is alive. A "number of different channels" are "being worked aggressively," he said.

Iran's previous president, Mahmoud Ahmadinejad, said he was willing to help find Levinson, and the family received what then-Secretary of State Hillary Clinton described in 2010 as "proof of life."

In 2011, the State Department said new evidence suggested that Levinson, who has diabetes and high blood pressure, was alive and being held somewhere in southwest Asia.

This year, a source with knowledge of the investigation told CNN, "We have every reason to believe that he's alive and that the Iranians control his fate."

Asked whether he believes the Iranian government is responsible for Levinson's disappearance, Kerry said he thinks the government "has the ability to help us here, and we hope they will."

McCain said he was "confident we are doing everything that we can" to get Levinson released from Iran,

He added that any negotiations in Levinson's case should also include attempts to free other Americans who are believed to be in Iranian custody.