The U.S.-born Saberi was sentenced on April 18 to eight years in prison in Iran on a charge of spying for the United States.
Saberi, 32, has been on hunger strike in Tehran's Evin prison since April 21. Her father, Reza Saberi, described his daughter as being "very, very weak and frail."
“Roxana has been significantly weakened by these seven days of hunger strike and we are very concerned for her health,” Reporters Without Borders said in a statement. “We are therefore symbolically taking over the hunger strike in a gesture of solidarity, so that she no longer has to go on.”
RSF says seven journalists and two bloggers are currently imprisoned in Iran.
Iran is ranked 166th out of 173 countries in the 2008 Reporters Without Borders press freedom index.