The United States called on Iran Sunday to immediately release US citizens and other foreigners detained on "fabricated" national security charges.

A State Department official issued the statement after an Iranian spokesman said an unidentified US citizen had been sentenced to 10 years in prison for alleged "infiltration" of the country.

"We call for the immediate release of all US citizens unjustly detained in Iran so they can return to their families," the official said, without making specific reference to a person.