Iran's police chief acknowledged Sunday that protesters detained in postelection unrest were abused in custody but said the deaths of prisoners were caused by illness, not torture. Iran's opposition has seized on claims of abuse at Kahrizak detention center, saying young people protesting President Mahmoud Ahmadinejad's June 12 re-election were tortured to death there. More troubling for the government, however, is that some prominent figures in its own conservative support base also say murders were committed in the prison and that those responsible should be brought to trial. The issue has come to the fore as Iran presses forward with a mass trial of more than 100 prominent reformist figures, opposition activists and others accused of offenses ranging from rioting to spying and seeking to topple the country's Islamic rulers. The trial, which has included televised confessions that rights groups say are likely extracted through pressure, is the government's latest attempt to crush the opposition. A senior commander of Iran's powerful Revolutionary Guard on Sunday called for the arrest and trial of opposition leader Mir Hossein Mousavi, his ally former President Mohammad Khatami and another reformist who ran for president, Mahdi Karroubi. Yadollah Javani said the three men have led what he called a "velvet coup" aimed at toppling Iran's clerical rulers. "If Mousavi, Khatami ... and Karroubi are the main elements of a velvet coup in Iran, which they are, it is expected that judicial bodies and intelligence officials go to them to put out the fire of sedition, arrest, try and punish them," he was quoted as saying by the official Islamic Republic News Agency.