A U.S. freelance journalist has been held in Iran since Jan. 31, ostensibly for buying a bottle of wine, and there has been no information about her for more than two weeks, her father said on Sunday.

Roxana Saberi, 31, an Iranian-American who was born in the United States and has reported for the BBC, NPR and other media, called her parents in North Dakota twice on Feb. 10, said Reza Saberi, her father.

"She said she was held in detention and we asked why. She said that she had bought a bottle of wine and that's why they are holding her there," he said by telephone from Fargo, North Dakota.

"We didn't say anything because we thought that this should be something very minor, but later on we found out ... that was just an excuse they make in order to arrest somebody."

Reza Saberi said he knew of no reason why his daughter had been detained.

"They don't tell us why they have done it. Sometimes they arrest journalists or others who are in the public to interrogate them, to see if they have any connections to America or government or to other governments," he said. "I don't know why they do. This is all speculation. Each case is different though."

He said he had not contacted the U.S. State Department because his daughter had asked him not to.

"The first conversation was very brief, just two or three sentences, then she called back and said please don't do anything, because they said that they are going to release me in two or three days," Reza Saberi said.

"We waited until we were forced to by these conditions, because we didn't have any news, any information," he said. "We were forced to make this public. Otherwise, we were hoping that it will be solved quietly without making it public."

He said Senator Byron Dorgan, a North Dakota Democrat, intended to contact the State Department on the family's behalf.

The State Department had no information on the case.

"There are people who are calling and telling us that we shouldn't worry," Reza Saberi said. "But since we don't know where she is held and why she is held, it's worrisome."

He confirmed that his daughter's credentials as a correspondent had been revoked but said she had stayed in Tehran to pursue a master's degree and was doing research for a book about Iranian society.

"She was interested in the culture and the people of the country and she was writing her own experiences, she has been there for six years," Reza Saberi said.