Reza Saberi, photographed in his home Feb. 28, 2009, has not heard from daughter Roxana since Feb. 10Iran says a U.S. journalist detained about a month ago is being held in the infamous Evin prison north of Tehran.

Iran's judiciary spokesman, Ali Reza Jamshidi, told reporters Tuesday that Roxana Saberi is being held in Evin on a court order, but he did not reveal the charges. The prison is Iran's largest and is also where prominent political prisoners are kept.

Iran's Foreign Ministry said Monday that the American journalist detained in Iran several weeks ago was engaged in "illegal" activities because she continued working after the government revoked her press credentials two years ago.

A U.S. State Department spokesman, Gordon Duguid, Tuesday said that Washington's intermediary in Iran, Switzerland, had not yet been able to verify Saberi's whereabouts. The spokesman said he asked for Iranian help in establishing contact with her and providing her access to legal advice.

The 31-year-old freelance journalist was detained in late January, and has had no contact with her family since early February.

Saberi's father said she told him in a brief phone call on February 10 she had been arrested for buying a bottle of wine, which is illegal in Iran.

The U.S. State Department has asked Iranian authorities for information on her case.

Saberi has been in Iran during the past six years. She has reported for U.S.-based National Public Radio, and for the BBC. She also was studying for a masters degree in Iranian studies.

Her father, Reza Saberi was born in Iran and lives in the north-central U.S. state of North Dakota. He said he last heard from his daughter when she called to say she was in detention but expected to be released within a matter of days.

Saberi's family said she was planning to move back to the United States later this year.