robert a levinson AP Photo/Manuel Balce Ceneta, File

President Donald Trump on Sunday responded to news from Iran that it had an „ongoing“ case against a former FBI agent who disappeared in 2007 under mysterious circumstances.

Robert Levinson, a former FBI agent, went missing from Kish Island in Iran on March 9, 2007.

He is considered to be the longest-held hostage in US history.

On Sunday, Iran offered its first admission that it had an open case against Levinson.

Trump responded by saying that returning Levinson would be a „very positive step.“

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President Donald Trump on Sunday responded to news from Iran that it had an „ongoing“ case against a former FBI agent who disappeared in Iran in 2007 under mysterious circumstances.

Robert Levinson, 71, had worked for the FBI before his disappearance from Kish Island, located off the southern coast of Iran, on March 9, 2007. In 2013, the Associated Press revealed that the man had been in Iran on an unsanctioned mission for the CIA, though the White House insisted he did not work for the US government at the time of his disappearance.

According to AP, the only photos that emerged of Levin since his disappearance came out in 2010 and 2011. He was last seen alive in a 2011 hostage video.

He is considered to be the longest-held hostage in US history.

The Trump administration last week offered a reward of up to $20 million for information about his whereabouts, in addition to an already existing $5 million offered by the FBI. Iran has not acknowledged that it was holding Levinson, though the State Department has claimed Levinson was taken hostage by the Iranian regime, according to AP.

On Sunday, Iran admitted for the first time that it had an open case against Levinson.

„According to the last statement of Tehran’s Justice Department, Mr. Robert Alan Levinson has an ongoing case in the Public Prosecution and Revolutionary Court of Tehran,“ Iran said in a filing to the United Nations obtained by AP.

Iran did not elaborate on the details of Levinson’s case, nor where he might be.

President Trump on Friday responded to the news, saying that it would be a „very positive step“ if Iran returned Levinson.

„At the same time, upon information & belief, Iran is, & has been, enriching uranium. THAT WOULD BE A VERY BAD STEP!“ he tweeted on Sunday.

Tensions between the US and Iran have intensified in recent months, after a series of hostilities occurred in the Gulf region. Iran also said last week that it had resumed uranium enrichment at its Fordow nuclear site, further pulling away from the 2015 nuclear agreement that the US walked away from last year.

The Trump administration has adopted a „maximum pressure“ campaign against Iran, ramping up waves of sanctions against Iran’s economy aimed at crippling its leadership.