By Jon Boyle
UPDATE 2: Call from reformist website follows death of protester in prison.
Iran's opposition urged senior clerics on Saturday to help secure the release of people arrested following June's disputed presidential election, after a protester died in prison.A reformist website said the son of an adviser to defeated conservative candidate Mohsen Rezaie had been killed in a Tehran prison after being detained in post-election unrest.
The authorities were not immediately available to confirm the death or the circumstances surrounding it.
Rights groups say hundreds of people, including senior pro-reform activists, journalists, academics and lawyers, have been arrested since Iran's disputed June 12 presidential vote.
In a flurry of announcements on websites, critics of the election condemned the tactics employed since the vote by the authorities, who have banned street protests by those who say the re-election of President Mahmoud Ahmadinejad was rigged.
Iran's top authority Supreme Leader Ayatollah Ali Khamenei endorsed the president's election victory soon after the vote.
But the opposition continues to contest the result of the election, which has plunged the country into its biggest internal crisis since the 1979 Islamic revolution and exposed deepening divisions in Iran's ruling elite.
"The only way out of this situation is ... to immediately release detainees," Ghalamnews quoted a joint statement issued by moderate defeated candidates and former President Mohammad Khatami as saying.
"We are very worried about their physical and mental health ... this imposed state security should end ... It is wrong to link pro-reform detainees to foreign countries," it said.
Tehran has accused western powers of fuelling post-election unrest, charges they deny, adding to tensions over Iran's nuclear programme which the West suspects is a cover for building atomic weapons. Iran says its programme is peaceful.
Israel, believed to be the Middle East's only nuclear power, has repeatedly described Iran's nuclear programme as a threat to its existence and the head of Iran's Revolutionary Guards said Iran would strike Israel's nuclear sites if targeted.
"If the Zionist Regime (Israel) attacks Iran, we will surely strike its nuclear facilities with our missile capabilities," Mohammad Ali Jafari, Guards commander-in-chief, told Iran's Arabic language al-Alam television.
The security establishment has thrown its support behind Ahmadinejad over the election and has been criticised by the opposition for its role in quelling the mass protests.
Moderate defeated presidential candidate Mehdi Karoubi said in a letter to Intelligence Minister Gholamhossein Mohseni-Ejei that those detained since the election had been subjected to "mental torture" and treated harshly, his website reported.
"The head of the executive body is not elected by the people's vote. The new government is illegitimate," he said in his letter.
"The intelligence network has turned into the most unclear and terrifying tool to suppress people ... detainees are being kept in illegal detention centres and are under mental torture. Physically they are threatened harshly," the letter added.
"Think of a way out of the current crisis, otherwise it will be difficult for you to manage Ramadan and other religious and national days," he added, referring to holidays when people gather and hold rallies.
Iranian official media have said at least 20 people died in violence after the poll.
Moderate defeated candidate Mirhossein Mousavi and the authorities blame each other for the bloodshed. Riot police and religious Basij militia eventually suppressed June's protests, but leading moderates have remained defiant, calling the new government "illegitimate".
Mousavi has said he will join a planned group of leading figures to preserve "people's votes", saying he would not allow his killed supporters' "blood to be trampled". (Reuters)