About 140 Iranians detained during protests against last month's disputed election result have been released from Evin prison, officials say. About 200 others, accused of more serious crimes, remain in the prison. The release comes after Iran's supreme leader ordered the closure of another detention centre because it failed to "preserve the rights of detainees". The unusual moves show how much pressure Iran's leaders are under over detainees, correspondents say. Officials also announced on Tuesday that 30 people were killed in clashes between opposition supporters and police - up from a previously stated figure of about 20. Speaking of the prison releases, National Security and Foreign Policy Committee member Kazem Jalali, quoted by Iranian news agencies, said: "Those who were released had committed lighter offences." ANALYSIS Jon Leyne Jon Leyne, Tehran correspondent The issue of opposition detainees arrested since the election has become the new focus of criticism of the Iranian government, even from former government supporters. Accounts from the opposition suggest that, at best, the prisons are unable to cope; at worst, there is systematic abuse of those detained. The government has always seen compromise as a sign of weakness, but it has finally been forced to give ground. The opposition will suspect that the closure of a prison and release of detainees is purely cosmetic, not a real change in policy. For the supreme leader it is a new humiliation. He has been reduced to ordering prison closures himself - usually the work of the president or the interior minister. With the president's inauguration for his second term expected in a few days, the pressure on the government can only increase. No well-known political figure was among the people released on Tuesday, he said. The committee is investigating the detentions. The leader of the judiciary has ordered a review of all cases of those held in prison since the election. 'Agents of unrest' Mr Jalali, quoted by Fars, said 150 people who remain in prison were suspected of carrying weapons and bombs, and vandalising public property during the unrest. A further 50 prisoners were described by judicial officials as the "agents of the unrest and some of them were members of anti-revolutionary groups," he told Fars. These 200 cases were still being investigated. Supporters of the protesters say the true number of people detained is much higher, possibly into the thousands. Memorial rally rejected They have also cast doubt on the number of people killed, believing it to be closer to 100. Opposition candidates Mir Hossein Mousavi and Mehdi Karroubi had requested permission to hold a memorial rally for the dead on Thursday, but they were refused by the interior ministry, Fars news agency reported. The prisoner releases from Evin came after a visit to the notorious prison by the committee, Mr Jalali said. Supporters of defeated candidate Mir Hossein Mousavi Mir Hossein Mousavi wanted his supporters to gather for a memorial Meanwhile, another detention centre - Kahrizak - was ordered to be closed "because it lacked necessary conditions to preserve rights of detainees," Mr Jalali was quoted as saying earlier by the semi-official Mehr news agency. It is not clear whether the detainees at the Kahrizak centre were released or transferred elsewhere. In recent days the opposition has reported almost every day new deaths of protestors held in prison. Iran's prisons are notorious for their poor conditions, correspondents report. Former political prisoners, such as journalists and bloggers, have complained of human rights abuses such as solitary confinement, harsh interrogation tactics and even torture at Evin.