It was the latest such standoff between security forces and opposition demonstrators who have been staging sporadic gatherings in defiance of the authorities over the disputed presidential election in June.
"People in groups of 20 or 30 shouted slogans as they passed by and I saw several arrested," the witness said.
Police were deployed in force around the office of reformist newspaper Etemad Melli, which belongs to defeated presidential candidate and former parliament speaker Mehdi Karroubi.
Karroubi has come under fire from hardliners over his controversial allegations that several people detained in the aftermath of the re-election of President Mahmoud Ahmadinejad were raped or tortured.
The Iranian authorities banned his newspaper from appearing on Monday after it printed the allegations of prison abuse, his aides said, adding that they hoped it would be published again on Tuesday.
But Tehran prosecutor's office said the newspaper will remain closed until "further notice" and denied earlier reports that Etemad Melli had not hit the stands owing to technical problems, Mehr news agency reported.
"In recent editions the newspaper has published material which is against national security," Mehr said, quoting a letter from the prosecutor's office to the press bureau at the culture ministry.
The prosecution said the ban came following the paper's "insistence on publishing illegal material" and that several complaints had been lodged against it, without elaborating.
Karroubi's son Hossein said on his father's party website earlier on Monday that a "temporary ban" against the newspaper was imposed because his father had printed "responses to insults against him" over the rape claims.
About 4,000 opposition supporters were arrested over the unrest that swept Tehran and other cities after the election which the opposition charges was rigged.
Most have since been released, but around 200 are thought to remain behind bars. Around 140 have also been put on trial at mass hearings before revolutionary courts which have been condemned by the West and opposition leaders as "show trials."
Officials say about 30 people were killed in post-election violence while the opposition has estimated that 69 people died.
The last major public clash was on August 5 when police in full riot gear broke up a rally by people protesting as Ahmadinejad was sworn in for a second four-year term before parliament.
Ahmadinejad is due to submit his cabinet to parliament on Wednesday, and has already said he will include at least three women ministers, a first in the Islamic republic.
However, some MPs have complained that he should be consulting them over the make-up of the cabinet, signalling divisions within the political elite that have been exposed in the post-election turmoil.
Karroubi, who came a distant fourth in the election, vowed on Sunday to seek the truth over the prison abuse allegations he first raised in a letter last month to influential cleric Akhbar Hashemi Rafsanjani.
"But I say again that this behaviour and intimidation will not silence me and I will raise the issues I deem necessary. I will only shut up when all the dimensions of these incidents have been examined and the people are told the truth."
Conservative parliament speaker Ali Larijani has dismissed the rape allegations as a lie and a hardline cleric called on Monday for Karroubi to be lashed over his claims.
"In religious teachings if someone accuses another of sexual crime and he is unable to prove it, then he should receive 80 lashes," Ahmad Khatami was quoted as saying by the Kayhan newspaper.
"Now Mr Karroubi has accused the regime and his allegations were rejected by two branches of the regime," said Khatami, a regular leader of Friday prayers in Tehran.
Iran has cracked down on opposition supporters and jailed scores of journalists, including the Iranian-Canadian reporter of the American magazine Newsweek over the past two months.
Another newspaper, Kalemeh Sabz (Green Word), which belongs to Ahmadinejad's main defeated rival Mir Hossein Mousavi, was shut down by the authorities in the immediate aftermath of the June 12 election.
