Many of those held at the Kahrizak facility were opposition supporters
Military prosecutors in Iran have charged three officials with killing three people held at a jail after presidential election protests.
They said the trio died at the Kahrizak detention centre after a series of beatings, Iran's Isna news agency said.
In total, the prosecutors issued indictments against 12 staff working at the facility south of Tehran.
President Mahmoud Ahmadinejad's re-election in June's poll triggered mass protests by opposition supporters.
The BBC's Tehran correspondent Jon Leyne, who is now in London, says most complaints about the treatment of the opposition have received angry denials from the government, particularly a number of allegations that male and female detainees have been raped by their prison interrogators.
It is not clear why the Iranian authorities have made even this small concession, our correspondent says.
One reason may be that one of the victims named by the government was a young man from a well connected Iranian family, whose death provoked outrage in ruling circles.
The suspicion from the opposition will be that this statement will just be followed by the prosecution of relatively low level officials - whereas many suspect that the maltreatment was ordered from much higher up, our correspondent adds.
'Bruises from beatings'
Isna quoted a prosecution office statement as naming the three killed as Mohsen Ruholamini, Amir Javadi and Mohammad Kamrani.
They were among more than 150 demonstrators taken to the centre, south of Tehran, in the aftermath of street protests, Isna added.
Officials had earlier said Ruholamini and Kamrani died of meningitis.
"The coroner rejected that these people died of meningitis and confirmed there were bruises on their bodies from beatings and that the cause of death was a series of beatings," the prosecution office's said.
Iran's government has said that at least 30 protesters have been killed in clashes since the election, which the opposition has described as rigged.
Some 200 anti-government protesters remain behind bars. At least five people have been sentenced to death, officials say.
The three officials charged in the Kahrizak case - whose names were not released - were among 12 officials facing prosecution over the inmates' deaths.
The Kahrizak centre was shut in July, after Iran's Supreme Leader, Ayatollah Ali Khamenei said it had failed to "preserve the rights of detainees".