Opposition supporters have broken off from official rallies to stage protests
Iran's authorities have banned foreign media from an annual rally due to be held on Monday, which they fear the opposition could use to stage protests.
Press permits were revoked for 7-9 December, officials said, and reporters told not to leave their offices.
Residents in the capital, Tehran, also said their internet access had been limited ahead of the rally.
Iran has cracked down hard on protests by opposition supporters following a disputed election in June.
Opponents of Iran's regime have taken to using officially sanctioned demonstrations to turn out in big numbers and publicise their message.
Rallies have been held annually on December 7 to mark the death of three students during an anti-American protest in 1953.
Iranian security forces including the elite Revolutionary Guards have warned that they will step in to prevent any attempt to use the event to stage opposition protests.
Ahead of the rally, Tehran residents said that they had been unable to use e-mail and that opposition websites were being more tightly restricted than before.
One official at the Iranian telecommunications ministry told Reuters news agency that internet and mobile phone connections would be disabled on Monday.
Thousands have been arrested and dozens killed this year after the disputed election of Mahmoud Ahmadinejad led to the largest street protests since the 1979 Islamic Revolution.
Dozens of people have been given jail terms and as many as five people have been sentenced to death over their alleged role in the demonstrations.
Press freedom group Reporters Without Borders said on Saturday that the situation for journalists in Iran was "getting worse by the day".
"Journalists who have chosen not to the leave the country are being constantly threatened or summoned by the intelligence services, including the intelligence service of the Revolutionary Guards," the group said in a statement.
"Some have been given long prison sentences at the end of completely illegal judicial proceedings."