Leading media rights group Reporters Without Borders (RSF) on Wednesday urged Iran to release a journalist arrested after closely covering a spate of mystery poisonings of schoolgirls, saying the detention appeared to be an attempt to silence him.
The spate of poisonings has affected over 5,000 pupils, mainly girls, since November, according to the authorities.
Rights groups based outside Iran have accused the authorities of failing to do enough to protect women's education and there were protests across Iran outside education authorities on Monday and Tuesday, according to monitors.
But supreme leader Ali Khamenei called Monday for the perpetrators of the "unforgivable crime" to be tracked down "without mercy".
Paris-based RSF said Ali Pourtabatabaei began covering the story for the Qom News website and on Twitter as soon as the first cases of poisoning were reported in the city of Qom at the end of November, and he was still covering the story when he was arrested on March 5.
It said he managed to phone his sister to tell her he had been arrested but it was not clear where he was being held.
Pourtabatabaei had criticized the lack of any reaction from the authorities in Qom to the first reported cases of poisoning, it added.
The mystery poisonings have intensified tensions in Iran almost six months into the protest movement sparked by the death of Mahsa Amini who had been arrested for allegedly violating the mandatory dress code for women.
Since the early days of the protest movement, Iran has held the two Iranian female journalists, Niloufar Hamedi and Elaheh Mohammadi, who helped expose the Amini story.
"As they already did with the journalists who revealed what happened to Mahsa Amini, the Iranian authorities are trying to silence those who dare to investigate and report other stories that are embarrassing for the government," said Jonathan Dagher, the head of RSF´s Middle East desk.
He said some 30 journalists and media workers were currently held by Iran. Most were arrested in the crackdown on the protest movement.
"Ali Pourtabatabaei must be released unconditionally... The systematic persecution of journalists who still dare to do their job must end," he said.
The interior ministry said in a statement on Tuesday "a number of people" suspected of manufacturing hazardous substances had been arrested in six provinces, including a pupil's parent.
With public anger rising, protests took place this week over the authorities' response in several cities including Tehran, Mashhad and Shiraz, Norway-based NGO Iran Human Rights (IHR) said.
It said authorities fired on protesters and arrested teachers to disperse a protest in the city of Sanandaj in western Iran.
