Activists in Iran say at least three demonstrators have died in jail in Tehran after being arrested during the recent protests.
Two members of the reformist wing of parliament named one detainee, Sina Ghanbari, saying he had died in Evin prison. Separately, human rights lawyer Nasrin Sotoudeh said at least two more protesters had also died in jail, but did not identify them.
Ms Sotoudeh does not believe Ghanbari killed himself, as the authorities maintain. "The authorities are responsible for the health of prisoners," she said. "I spoke to a prisoner in Evin prison and I was told three detainees had lost their lives. When authorities resort to mass arrests, they cannot claim to protect their rights. It is not possible in such a situation for the judicial process to take its due course."
The outspoken reformist politician Mahmoud Sadeghi on Tuesday said about 3,700 people – a far higher number than originally thought – were arrested over the 10 days of the protests. The Iranian parliament's official website, icana.ir, quoted him as saying it was difficult to keep track of the exact number of those detained because different security and intelligence forces were involved.
Mr Sadeghi did not say where the figure of 3,700 came from but it would constitute nearly 10 per cent of the 42,000 people which the Iranian interior minister says took part in the protests. Previously, authorities have said "hundreds" were arrested in Tehran alone, but not offered a nationwide figure.
There is also concern over unofficial detention centres like Kahrizak, which was used to hold those arrested during the 2009 protests. It emerged afterwards that a number of them had been tortured and killed there.
"I warn the president, intelligence and judicial officials against the repeat of a second Kahrizak," Mr Sadeghi said on Twitter.
On Sunday, Tehran prosecutor Abbas Jafari Dolatabadi said that 70 of those held have been released on bail during the last 48 hours. He added that there would be more releases, except for the main instigators of the riots, who will be "dealt with seriously". At a closed session, senior security officials briefed parliament on the protests and the conditions of the detainees, the state-run IRNA news agency reported.
Iran's supreme leader, Ayatollah Ali Khamenei, on Tuesday blamed "Americans and Zionists" for the protests but president Hassan Rouhani has alluded to the authorities being out of touch with the youth of the country. Officials say the average age of those arrested was 25. By contrast, most of those taking part in the pro-government rallies over recent days have been middle-aged or older men.
The United States and Israel have expressed support for the protests, which began on December 28 in Iran's second largest city, Mashhad, but deny Iranian government allegations that they fomented them.
US officials and analysts studying Iran said they believed conservative opponents of Rouhani, a relative moderate within Iran's clerically overseen government, started the demonstrations in Mashhad but quickly lost control of them.
Iranian authorities have said that the protests are waning. That is in part due to the government blocking access to the popular messaging app Telegram, which demonstrators used to share images of the rallies and organise. Authorities also have deployed additional police and members of the Basij, a volunteer organisation affiliated with Iran's paramilitary Revolutionary Guard.