An American Navy veteran who has been detained by Iran since 2018 and is serving a 13-year sentence was released on medical furlough Thursday, Secretary of State Mike Pompeo announced.

Michael White's release on humanitarian grounds was conditioned upon him staying in Iran. He is now in the custody of the Swiss embassy where he will undergo a medical evaluation.

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"The United States will continue to work for Michael’s full release as well as the release of all wrongfully detained Americans in Iran," Pompeo said in a statement.

White is seen with his mother, Joanne White, in a photo released by his laywer Mark Zaid. (White family via AP)

White’s family has said he traveled to Iran to visit his girlfriend — the two met online — and was arbitrarily detained. He previously served in the Navy for 13 years.

White, the first American known to be detained in Iran since President Trump took office, is accused of insulting Ayatollah Ali Khamenei and posting a photo on his social media.

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A spokesman for the White family said the family was grateful to the Iranian government for an “interim humanitarian step.”

“We continue to urge them to release Michael unconditionally so that he can return to the United States to receive the advanced medical care he needs,” spokesman Jon Franks said.

American Navy veteran Michael R. White was detained in Iran after visiting his Iranian girlfriend, his mother said. (Instagram)

His release comes as Iran struggles to contain the coronavirus pandemic that has gripped the hardest-hit Middle Eastern country.

Iran reported 147 deaths on Wednesday – a nearly 15 percent jump – raising the country's overall death toll to 1,135 amid a total of 17,361 confirmed cases. The government's response to the outbreak has faced widespread criticism that Iran acted too slowly and might even have covered up initial cases.

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Iran this week announced it had temporarily freed some 85,000 inmates from its overcrowded and dilapidated prisons in a effort to contain the virus' rapid spread through the system.

White was the second American to be released from detainment in the Middle East this week.

Amer Fakhoury, a naturalized U.S. citizen from New Hampshire, was detained during a family vacation in Lebanon six months ago. He was beaten and tortured while detained, and finally released from prison Thursday.

In announcing White's medical furlough, Pompeo again called upon the Iranian government to immediately release on humanitarian grounds the Iranian-American businessmen Morad Tahbaz, Baquer Namazi, and Siamak Namazi.

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He also asked Iran to work with the U.S. for the return of Robert Levinson, a former FBI agent who mysteriously disappeared in 2007.

Fox News' Victor Garcia and The Associated Press contributed to this report.