"As the Iranian regime continues its crackdown on the protests initiated by Mahsa Amini's death, almost half of all newly arrested journalists are women, including two who are facing the death penalty," said Reporters Without Borders (RSF).
"The increasing detention of female journalists symbolically reveals the Iranian regime's intention to systematically silence women's voices," it said in a statement.
The Islamic republic has been gripped by protests that erupted when Amini, 22, died in custody on September 16 after her arrest for an alleged breach of Iran's strict dress code for women.
This week, it indicted Niloufar Hamedi and Elahe Mohammadi, two newspaper journalists who first drew public attention to Amini's death, for "propaganda against the system and conspiracy to act against national security" -- charges that can carry the death penalty.
RSF said it was "deeply concerned about the fate of these journalists who risk paying a very high price, including the death penalty, for having had the courage to reveal a truth that the authorities seek to stifle.
"They must be released immediately and unconditionally."
Since the protests erupted, at least 42 journalists have been arrested across Iran, RSF said.
So far eight of them have been released, and women account for 15 of the 34 still in detention, the Paris-based organisation added.
"There are now five times more women imprisoned than before the protests started. The number of detained female journalists has never been so high."
RSF said the cases of Hamedi and Mohammadi were of particular concern.
"Niloufar Hamedi and Elahe Mohammadi... have now been imprisoned for more than a month and have been charged with accusations that could result in the death penalty," it said.
Hamedi, who reported for the reformist Shargh newspaper from the hospital where Amini was in a coma before she died, was arrested on September 20.
Mohammadi, a journalist who went to Amini's hometown of Saqez to cover her funeral for the Ham Mihan newspaper, was detained on September 29.
The watchdog also raised concern about Nazila Maroufian, a reporter for the Rouydad24 news website who was arrested on November 4 after interviewing Amini's father.
In the interview published on the Mostaghel website, Amini's father denied she had any health issues, as claimed by the authorities.
RSF said a total of 48 journalists were now behind bars in Iran, making the Islamic republic the third largest jailer of journalists in the world after China and Myanmar.
This story has been published from a wire agency feed without modifications to the text. Only the headline has been changed.
