Iran on Tuesday confirmed it was holding a freelance US journalist with Iranian nationality in a Tehran prison but did not reveal the charges.
"The arrest (of Roxana Saberi) took place on a writ issued by the revolutionary court," judiciary spokesman Ali Reza Jamshidi told reporters.
"I do not know exactly what the accusations are," Jamshidi said, adding that Saberi, 31, is being detained in Tehran's Evin prison.
Iranian foreign ministry spokesman Hassan Ghashghavi said on Monday that Saberi was working "illegally" in the country after her press identity card was revoked in 2006. He did not however confirm or deny her arrest.
American media, citing Saberi's father, reported last week that the US-born journalist was arrested in late January on charges of buying alcohol, which is prohibited in the Islamic republic.