"The Iranian regime continues to hold US citizens and other foreigners captive on bogus charges related to national security," Efe quoted a US State Department official as saying.
The unnamed official also called for the "immediate liberation of all US citizens unjustly detained in Iran."
"All US citizens, especially those of dual nationality, who are considering a trip to Iran, should read carefully our latest travel warning," the source said.
As reported in various US media, a person of US nationality, whose identity has not been released, was sentenced Saturday to 10 years in prison in Iran for entering that country surreptitiously to "gather information."
Last October two US citizens, Siamak Namazi and his father, Baquer Namazi, who also have Iranian nationality, were sentenced to prison in Iran. Washington has been demanding their release ever since.
In January 2016, Tehran authorities freed The Washington Post reporter Jason Rezaian and another three Iranian-American citizens in exchange for the US dropping charges against seven Iranians.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)