Roxana Saberi in Bam, 1,250 kilometres southeast of Tehran, in March 2004. ((Reuters))

The American journalist on a hunger strike for two weeks to protest her imprisonment in Iran was briefly hospitalized after she intensified her fast by refusing to drink water, Reporters Without Borders said Monday.

The press freedom group said 32-year-old Roxana Saberi was taken Friday to a clinic at Tehran's Evin prison, where she has been held since her arrest in January. She was released from the clinic within a day after again drinking water, the group said.

Saberi's Iranian-born father, who travelled to Iran to seek his daughter's release, said last month that she was drinking only sweetened water while refusing food to protest her eight-year jail sentence for allegedly spying for the U.S.

Reporters Without Borders said Reza Saberi told the group over the weekend that his daughter stopped drinking water after Iranian authorities denied she was on a hunger strike.

"Following that, she decided to do a complete hunger strike," Soazig Dollet of the Paris-based group told The Associated Press. "So she was really weak and went to the clinic inside the prison for the day, but not more than a day."

Saberi's father did not answer phone calls seeking comment on Monday.

Saberi, a dual Iranian-American citizen, has lived in Iran for six years. She was born in the U.S. and grew up in Fargo, N.D.

She was initially accused of working without press credentials, but authorities later made the more serious charge that she passed intelligence to the U.S. She was convicted on the espionage charge after a one-day trial behind closed doors.

The administration of U.S. President Barack Obama has called the allegations baseless and demanded her immediate release.

The case has been a source of tension between the U.S. and Iran at a time when Washington is reaching out to Tehran after decades of diplomatic stalemate.

Iran promises fair appeal

Saberi was working as a freelance reporter for organizations including National Public Radio and the British Broadcasting Corp. before her arrest.

Iranian authorities have promised a fair review of her appeal while calling for an end to what they consider outside interference from groups like Reporters Without Borders.

Four of the journalist group's members, including its secretary-general, began their own hunger strikes a week ago in support of Saberi, while urging her to end her own protest out of concern for her health.

In Tehran on Monday, Foreign Ministry spokesman Hasan Qashqavi said the group's protest was not welcome.

"Iran's judiciary is an independent body and any foreign attempt to intervene in it goes against international measures," he told reporters in his weekly briefing.

"This is not a complicated issue. This Iranian lady has got a sentence and should wait and see what verdict the appeals court will issue," he said.