Protests have continued since June's presidential election
Iranian officials have blocked two opposition leaders from holding a memorial rally for people killed during post-election violence last month.
Mir Hossein Mousavi and Mehdi Karroubi were refused a permit by the Interior Ministry for a rally on Thursday, Fars news agency reported.
At least 20 people died in days of violence after last month's election.
Meanwhile, Iran's supreme leader has ordered the closure of a detention centre where protesters were held.
The semi-official news agency Fars quoted an Interior Ministry official as saying: "We have received a request signed... by two presidential election candidates who were not popular amongst the majority of voters asking, as two individuals, for a permit to hold a memorial service for those who were killed in the post-election incidents."
The permit was not issued, he said.
Protests erupted after the 12 June presidential election, in which the incumbent, Mahmoud Ahmadinejad, was declared winner.
Apart from the deaths, thousands of protesters were detained, with many still in prison weeks later.
Supreme Leader Ayatollah Ali Khamenei ordered the closure of the jail at Kahrizak, saying it had failed to "preserve the rights of detainees".
Ayatollah Ali Khamenei has the final say in many areas
The highly unusual move shows how much pressure Iran's leaders are under over detainees, correspondents say.
The leader of the judiciary has ordered a review of all cases of those held in prison since the election, and the parliament has set up a committee to investigate the issue.
"Kahrizak is the detention centre which the leader ordered closed because it lacked necessary conditions to preserve rights of detainees," said Kazem Jalali, spokesman of the committee, quoted by the semi-official Mehr news agency.
It is not clear whether the detainees at the Kahrizak centre were released or transferred elsewhere.
There are also continuing reports of grim conditions inside Tehran's main prison, Evin, which seems unable to cope with the large number of opposition supporters rounded up since the election, says the BBC Tehran correspondent Jon Leyne.
In recent days the opposition has reported almost every day new deaths of protestors held in prison.
One of those who died was the 25-year-old son of Abdolhossein Rouhalamini, a close aide to one of the opposition candidates, Mohsen Rezai.
Mohsen Rouhalamini was arrested during a protest on 9 July, was taken to a hospital after two weeks and died, Associated Press news agency reported.
An opposition news website said he had been held at Kahrizak, and that his face was beaten.
But the head of Tehran prisons, Sohrab Soleimani, said the aide and another prisoner had died of meningitis.
The death of someone so close to the ruling circle has obviously shocked senior figures in Iran, our correspondent says.
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.