The White House said on Thursday that missing former FBI agent Robert Levinson may have died in Iran, acknowledging his family's conclusions, AFP reported.
Iran, however, claimed Levinson had left the country years ago.
Levinson’s family said on Wednesday that US intelligence had convinced them that he died in Iranian custody but that it was unclear when or how.
"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. We don't know when or how he died, only that it was prior to the COVID-19 pandemic," they said in a statement.
President Donald Trump did not confirm Levinson's death when asked by reporters late Wednesday but his national security advisor, Robert O'Brien, went further Thursday.
"Iran must provide a complete accounting of what occurred with Bob Levinson. While the investigation is ongoing, we believe that Bob Levinson may have passed away some time ago," O'Brien said, according to AFP.
Secretary of State Mike Pompeo, in a cautious separate statement, said, "Only Iran knows for certain what happened to Bob since his abduction more than 13 years ago."
Both Pompeo and O'Brien renewed demands that Iran release several US citizens who remain in jail.
Levinson vanished in Iran in 2007 while on an unauthorized CIA mission. In the past, Iran insisted that Levinson is not in the country and that it has no further information about him, but in November it acknowledged for the first time it has an open case before its Revolutionary Court regarding Levinson.
Iran's foreign ministry spokesman Abbas Mousavi implicitly denied on Thursday the family's claim that Levinson died in Iranian custody.
"Based on credible evidence, (Levinson) left Iran years ago for an unknown destination," Mousavi said in a statement quoted by AFP.
He added that Iran had done everything it could to trace what happened after he left but found "no evidence of him being alive."
Mousavi called on Washington to make an official announcement if Levinson's death was confirmed, without "politicizing and exploiting the family's feelings."
Alireza Miryousefi, Iran's chief press officer at the United Nations, had said earlier that Tehran had "no knowledge" of Levinson's whereabouts.
Levinson's family in 2017 filed a lawsuit against the Iranian government in the United States. The lawsuit seeks unspecified damages from Iran, in part for inflicting emotional distress on Levinson’s wife and seven children.