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The family of former FBI agent Robert Levinson, who disappeared 13 years ago on an island off Iran, said Wednesday that he died while being held in Iran as the longest-held hostage in American history.

"We recently received information from US officials that has led both them and us to conclude that our wonderful husband and father died while in Iranian custody," his family said in a statement Wednesday.

Relatives said they did not know how or when he died, "only that it was prior to the COVID-19 pandemic."

The World Health Organization declared the virus outbreak a pandemic on March 11. On March 9, the FBI's Washington field office noted the anniversary of Levinson's disappearance and called the date "another opportunity for the leadership of the government of Iran to finally return Bob home to his family." The family apparently received the latest information after that.

A photo provided by the family of retired FBI agent Robert Levinson after they received it in April 2011. Levinson family via AP

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Alireza Miryousefi, spokesman at Iran's Permanent Mission to the U.N., said Wednesday: "Iran has always maintained that its officials have no knowledge of Mr. Levinson's whereabouts, and that he is not in Iranian custody. Those facts have not changed."

President Donald Trump expressed his sympathies to the family when asked about the statement at the White House coronavirus briefing, but he said the U.S. did not yet have confirmation that Levinson is dead.

"It's not looking promising," Trump said, but "I won't accept that he's dead. They haven't told us that he's dead. But a lot of people are thinking that is the case."

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Levinson, who spent 22 years with the FBI, disappeared March 9, 2007, during a business trip on Iran's Kish Island. At the time, the U.S. government maintained that he was there on his own. But six years later, federal officials reluctantly admitted that he was there doing contract work for the CIA.

At the time of the disclosure, his family said the U.S. government failed to make his recovery the priority it should have been.

The only known traces of Levinson surfaced in 2011 when family members released still photos and a video in which he pleaded for help.

"I have been held here for 3½ years. I am not in very good health. I am running very quickly out of diabetes medicine," he said in the recording.

Iranian officials steadfastly denied knowing anything about him, despite queries from the U.S. and requests through other countries that had better relations with Iran.

"Those who are responsible for what happened to Bob Levinson, including those in the US government who for many years repeatedly left him behind, will ultimately receive justice for what they have done," the family's statement said.