More than 145 people detained after Iran's disputed June election were kept for several days in a room of 70 square metres at a Tehran jail, including three who died, a parliamentary report was quoted as saying.
In rare official criticism of the treatment of post-vote detainees, the investigative committee's report said Tehran's then prosecutor Saeed Mortazavi ordered the group transferred to Kahrizak detention centre, despite a lack of space there.
The report into the situation in Kahrizak after the election, read out in parliament and cited by Iranian media, said the space where the detainees were held lacked proper ventilation and sanitary conditions.
It rejected the initial claim by officials, including Mortezavi, that the three deaths were caused by meningitis, ILNA news agency said.
"Their deaths are attributed to various issues such as limitation of space, poor sanitary conditions, inappropriate nutrition, heat, lack of ventilation and ... also as a result of physical attacks," ILNA reported.
Kahrizak was closed in July on the orders of Supreme Leader Ayatollah Ali Khamenei after at least three people, arrested during widespread unrest after the vote, died in custody there.
Last month, Iranian media said the judiciary had charged three Kahrizak officials with the murder of three pro-reform protesters arrested after the June 12 election, which plunged Iran into deep and ongoing political turmoil.
But the report also dismissed opposition accusations that some Kahrizak detainees had been sexually assaulted, ILNA said.
"The committee arrived at no instances of sexual molestation and we reject the claim strongly," it said.
The investigative committee consisted of at least six members of parliament, both conservative and moderate MPs.
Citing the committee's report, the semi-official Mehr News Agency said Mortazavi had ordered the transfer of 147 post-election detainees from Tehran's Evin jail to Kahrizak, south of the capital.
"According to this report, Kahrizak officials first refrained from accepting the detainees because of the lack of availability of any space, but ultimately they were forced to take in the 147 detainees into a space of merely 70 square metres (750 sq ft) at the insistence of (Mortazavi)," Mehr said.
"The detainees were kept for four days ... in this room without enjoying proper ventilation, suitable food and sanitary conditions and also in very hard punitive conditions," it said, without elaborating.
Mortazavi, a hardliner who played a key role in mass trials of leading reformers after the election, was replaced as Tehran chief prosecutor in late August and named Iran's deputy prosecutor general.
He signed indictments against dozens of pro-reform figures put on trial on charges of inciting protests in a bid to topple the Islamic establishment after the election. Moderates also blame him for shutting down publications critical of the government during his six years as Tehran prosecutor.
There was no immediate comment from Mortazavi on the report.
The head of parliament's foreign policy and national security committee, Alaeddin Boroujerdi, said that with the report the assembly had carried out its supervisory role and that it was now for the judiciary to take "relevant measures", ISNA news agency reported.
The June poll, which secured President Mahmoud Ahmadinejad's re-election, sparked Iran's biggest unrest since the 1979 Islamic revolution. Authorities deny allegations of vote-rigging.
Thousands of people protesting against the conduct of the election were arrested and some were beaten in detention. Most of them have since been released, though more than 80 people have received jail sentences of up to 15 years.