Since the overwhelming election victory for incumbent President Mahmoud Ahmadinejad there have been reports of opposition members being arrested, newspapers being censored and banned and internet sites being blocked.
Hundreds of thousands of defeated presidential candidate Mir Hossein Mousavi took to the streets on Monday, 15 June, defying a protest ban. Gunfire was heard and at least one person is reported to have been killed and many wounded.
Until his appearance earlier at Monday's rally, Mr Mousavi, had not been seen in public since Friday's poll, sparking fears he was under house arrest.
Reports of the protests have been censored on TV and in the newspapers
His wife, Zahra Rahnavard, earlier attended a rally of students in Tehran.
Overnight on Sunday dozens of students were arrested during a protest at their university.
Iran's deputy police chief, Ahmad Reza Radan, told the official Islamic Republic News Agency (IRNA) that about 170 people were arrested over the weekend.
Reports said that among the opposition politicians and activists rounded up were Mohammad Reza Khatami, brother of former President Mohammad Khatami.
AFP names Behzad Nabavi, a former deputy parliament speaker, Mohsen Mirdamadi, who headed parliament's foreign policy commission under Khatami, and Khatami's government spokesman Abdollah Ramezanzadeh as having been detained.
Radio Free Europe spoke to the wife of religious activist Taghi Rahmani, who described how her husband was taken away in a car by security forces from their home on Sunday night.
However, a number of news agencies, including the Associated Press, say that a number of people were released on Sunday and Mohammad Reza Khatami is mentioned as being among them.
It is not known how many remain in custody.
There has been a filtering of many web sites, censorship of newspapers before printing, and restrictions on the broadcast of news of the three losing candidates, according to the reformist newspaper Aftab-e Yazd.
Sarmayeh, another reformist newspaper, has reported that Kalameh Sabz (Green Word), the paper run by Mir Hossein Mousavi, was nowhere to be found in Tehran on Monday. The Associated Press is quoting an unnamed editor as saying that the paper was blocked at the printing house because the authorities were upset with statements by Mr Mousavi reported in it.
Sarmayeh's censored article on Green Word also discussed the suspension of Velayat, a newspaper circulating in Qazvin, a town to the west of Tehran.
According to Reporters Without Borders, a Paris-based group that campaigns for press freedom, a number of leading journalists had been arrested. They included Reza Alijani, Hoda Sabaer, Ahamad Zeydabadi and Taghi Rahmani.
There is no word of about 10 other journalists who have either been arrested or gone into hiding, the group says.
Over the last few days, fours of the main pro-reform newspapers have been closed or prevented from questioning the official election results.
Two Farsi-language TV stations were partially jammed on Sunday.
Reporters Without Borders said the editor of the news website Nooroz, Said Shariti, has been arrested and 10 or so pro-opposition websites have been censored.
The organisation reports that the internet has been very slow, as has the mobile phone network.
YouTube and Facebook are hard to access and pro-reform sites such as Khordadeno, AftabNews and Ghalamesabz have at times been completely inaccessible.
There have also been reports of a clampdown on independent media.
The Saudi-funded Arabic TV station al-Arabiya said its offices in Iran were shut down for "unknown reasons" for one week.
Reporters Without Borders says the Farsi-language satellite broadcasts of Voice of America were blocked over the weekend.
Access to the BBC's Persian-language satellite TV channel and the BBC's news website has been curbed.
German television network ZDF said on Sunday that its reporter in Iran and other reporters were being "prevented from doing their jobs in a massive form". The network said it was unable to show a broadcast feed from the network's correspondent depicting protests.
Italian state TV RAI said one of its crews was caught in a street clash. An Iranian interpreter was beaten by riot police and officers confiscated the cameraman's videotapes.
A spokesman for the Swedish network SVT said its reporter in Iran had been asked to "leave Iran as soon as possible because the elections are over".