The White House condemned Iran for taking hostages in a statement Friday, warning that there would be "serious consequences" if the country didn't release Americans it is holding.

"For nearly forty years, Iran has used detentions and hostage taking as a tool of state policy," the statement said.

"Iran is responsible for the care and well-being of every United States citizen in its custody. President Trump urges Iran to return Robert Levinson home, who has been held for over 10 years, and demands Iran release Siamak and Baquer Namazi, who were taken during the Obama administration, along with all other American citizens unjustly detained by Iran."

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Levinson is a former FBI agent who went missing in the country more then 10 years ago. Iranian-Americans Siamak and Baquer Namazi were also sentenced to prison in the country.

The statement also mentioned Chinese-born U.S. citizen Xiyue Wang, who was sentenced Monday to 10 years in prison for espionage.

Wang was in Iran doing research for his doctoral dissertation in history at Princeton University when he was arrested last summer.

"President Trump is prepared to impose new and serious consequences on Iran unless all unjustly imprisoned American citizens are released and returned," the statement concluded.

Iran and the U.S. have a long history of struggles negotiating the release of hostages.

From 1979 to 1981, 53 hostages were held at the U.S. Embassy in Tehran. The hostage crisis became a staple of the nightly news and was a foreign policy nightmare for then-President Jimmy Carter, contributing to his election loss in 1980.

In early 2016, Iran released four U.S. citizens, including Washington Post reporter Jason Rezaian, 39, who had been incarcerated for the prior 18 months.

Trump knocked presidents for spending money to free hostages on the campaign trail, even taking credit for the release of Rezaian and other captives in 2016.