TEHRAN Iran's Revolutionary Guards, who helped quell protests after the June election, warned the opposition on Monday not to use anti-U.S. rallies this week to stage new demonstrations.
Moderate opposition leader Mirhossein Mousavi appeared to urge his supporters on Saturday to take to the streets on November 4, the 30th anniversary of the U.S. embassy takeover in Tehran.
The authorities, seeking to avoid any repeat of the huge demonstrations that erupted after the disputed election in June won by President Mahmoud Ahmadinejad, say security forces will confront any illegal gatherings.
The Guards called on the Iranian people to "exercise vigilance in regard to the likelihood of mischief and plots by the enemy's agents and some unaware and misguided people on November 4," the official IRNA news agency reported.
"The Iranian nation will not allow any group to impose itself and use diversionary and false slogans on Wednesday," it quoted a Guards statement as saying.
Anti-Western rallies usually take place outside the old U.S. embassy -- now called the "den of espionage" in Iran -- to mark the day in 1979 when radical students scaled its walls and took 52 Americans hostage.
Some reformist websites have called on people to gather outside the Russian embassy instead, apparently to protest against Moscow's swift recognition of Ahmadinejad's election victory.
On Monday, authorities closed down the business newspaper Sarmayeh, critical of Ahmadinejad's economic policies.
IRNA said the daily was closed because of repeated violations of press laws.
The Intelligence Ministry said five "terrorist" suspects alleged to have planned to assassinate an official ahead of the anti-U.S. rallies had been arrested, state television reported.
In a warning to opposition leaders, deputy police chief Ahmadreza Radan said: "Those who encourage people ... to stage gatherings will have to answer for their actions."
The powerful Guardian Council, Iran's top legislative body, threw its weight behind the authorities' message.
It was confident "the revolutionary youth will not allow a domestic group linked to foreign oppressors and lawbreakers to blemish this great day," media quoted a statement as saying.
In September, opposition demonstrators clashed with government supporters and police at annual pro-Palestinian rallies.
The June 12 election was followed by Iran's worst unrest since the Islamic revolution three decades ago, exposing deep divisions in the establishment.
The Guards and an allied Islamic militia suppressed the protests and thousands were arrested. Many of them have been put on trial, including several former government figures.
The authorities deny vote rigging, and have portrayed the unrest as a foreign-backed attempt to undermine the Islamic state.
The opposition says more than 70 people were killed in the post-election violence. Officials say the death toll was half that and members of the security forces were among the victims.
Supreme Leader Ayatollah Ali Khamenei said last week it was a crime to question the election.
A senior adviser to Khamenei on Monday urged "people standing against the revolution and its leadership" to return to the embrace of the Islamic establishment, the ISNA news agency reported.
"Otherwise our nation ... will isolate them," said Yahya Rahim-Safavi, a former Guards commander-in-chief.
Washington cut diplomatic ties with Tehran during the hostage crisis in 1980.
(Additional reporting by Hashem Kalantari; Editing by Andrew Dobbie)