A rally against the re-election of Iranian President Mahmoud Ahmadinejad is being held in defiance of a ban on protests, AFP reports from the scene.
The news agency says hundred are taking part in the Tehran rally. It follows a weekend of unrest over the poll.
Defeated candidate Mir Hossein Mousavi said on his website that he would attend to urge supporters to keep calm.
Mr Mousavi wants election results annulled, alleging widespread fraud. Mr Ahmadinejad says the vote was fair.
Tens of thousands rallied in Tehran on Sunday to celebrate his victory.
Following two days of unrest, the interior ministry said on Monday: "Some seditious elements had planned to hold a rally."
It added: "Any disrupter of public security would be dealt with according to the law."
Mr Mousavi's campaign initially announced that the event had been called off, but his website later said he would address the crowd.
The BBC's Jon Leyne, in Tehran, says he understands plain-clothed militias have been authorised to use live ammunition for the first time.
Ahead of the rally, correspondents said life appeared to be returning to normal in central Tehran. Shops were open and there was little evidence of the weekend's unrest.
I urge you, Iranian nation, to continue your nationwide protests in a peaceful and legal way
Mir Hossein Mousavi
Editors' blog: Stop the jamming
Internet brings events to life
John Simpson's view
Challenge to republic
However, there was a small demonstration attended by Mr Mousavi's wife Zahra Rahnavard at Tehran University.
She said the campaign was continuing, and urged people to go onto their roofs shouting "God is great".
Reports said paramilitaries were trying to break up the demonstration, and that students had taken cover in a mosque.
The campus has been a focus of unrest in recent days. Overnight police and militias raided dormitories, arresting dozens of students.
In related developments:
President Ahmadinejad reportedly cancelled a trip to Moscow, where he was due to attend a regional summit on Monday
Reports say Mr Mousavi's newspaper Kalameh Sabz has suspended circulation
About 200 relatives of detained demonstrators took part in a protest outside Tehran's Revolutionary Tribunal calling for their release, AFP news agency reported.
International concern
On Sunday Mr Mousavi's website carried a statement saying he had formally called on Iran's Guardian Council ,which must certify the counting, to annul the election.
He added: "I urge you, Iranian nation, to continue your nationwide protests in a peaceful and legal way."
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Police on motorbikes charge protesters (Courtesy Corriere della Sera TV) - events like these are being filmed on mobile phones and uploaded online
Another defeated candidate, Mohsen Rezaie, also officially contested the results. The Guardian Council said it would rule on both complaints within 10 days.
Late on Sunday Mr Mousavi met Iran's Supreme Leader, Ayatollah Ali Khamenei, to pursue his case against the results of Friday's election.
Mr Khamanei's office said he had told the candidate that "complaints should be followed through legal channels" and urged Mr Mousavi to "follow the issue calmly".
POST-POLL CRACKDOWN
More than 100 opposition figures arrested, including the brother of ex-reformist President Khatami.
Local and international phone and text message services interrupted
Social networking and newspaper websites blocked
BBC says "heavy electronic jamming" from inside Iran disrupts its Persian TV service
International journalists arrested and asked to leave
Iranian newspapers do not carry reports of the violence
Source: Various reports
Sunday saw clashes between the police and anti-Ahmadinejad protesters in several parts of Tehran for a second day.Police hit protesters with batons and charged them on motorbikes.
Mousavi supporters cried "death to the dictator" into the evening. Scores of people are reported to have been arrested.
Mr Ahmadinejad dismissed the unrest as "passions after a soccer match".
Foreign powers have expressed concern about the election.
In an interview on US television, Vice-President Joe Biden said: "It sure looks like the way they're suppressing speech, the way they're suppressing crowds, the way in which people are being treated, that there's some real doubt."
German Foreign Minister Frank-Walter Steinmeier said he had summoned the Iranian ambassador to explain the election.
"There are a lot of reports about electoral fraud," he said.
French Foreign Minister Bernard Kouchner said: "I am sorry that instead of openness there has been a somewhat brutal reaction."
But Mr Ahmadinejad was congratulated by the presidents of Iraq, Afghanistan and Venezuela.
The news agency says hundred are taking part in the Tehran rally. It follows a weekend of unrest over the poll.
Defeated candidate Mir Hossein Mousavi said on his website that he would attend to urge supporters to keep calm.
Mr Mousavi wants election results annulled, alleging widespread fraud. Mr Ahmadinejad says the vote was fair.
Tens of thousands rallied in Tehran on Sunday to celebrate his victory.
Following two days of unrest, the interior ministry said on Monday: "Some seditious elements had planned to hold a rally."
It added: "Any disrupter of public security would be dealt with according to the law."
Mr Mousavi's campaign initially announced that the event had been called off, but his website later said he would address the crowd.
The BBC's Jon Leyne, in Tehran, says he understands plain-clothed militias have been authorised to use live ammunition for the first time.
Ahead of the rally, correspondents said life appeared to be returning to normal in central Tehran. Shops were open and there was little evidence of the weekend's unrest.
I urge you, Iranian nation, to continue your nationwide protests in a peaceful and legal way
Mir Hossein Mousavi
Editors' blog: Stop the jamming
Internet brings events to life
John Simpson's view
Challenge to republic
However, there was a small demonstration attended by Mr Mousavi's wife Zahra Rahnavard at Tehran University.
She said the campaign was continuing, and urged people to go onto their roofs shouting "God is great".
Reports said paramilitaries were trying to break up the demonstration, and that students had taken cover in a mosque.
The campus has been a focus of unrest in recent days. Overnight police and militias raided dormitories, arresting dozens of students.
In related developments:
President Ahmadinejad reportedly cancelled a trip to Moscow, where he was due to attend a regional summit on Monday
Reports say Mr Mousavi's newspaper Kalameh Sabz has suspended circulation
About 200 relatives of detained demonstrators took part in a protest outside Tehran's Revolutionary Tribunal calling for their release, AFP news agency reported.
International concern
On Sunday Mr Mousavi's website carried a statement saying he had formally called on Iran's Guardian Council ,which must certify the counting, to annul the election.
He added: "I urge you, Iranian nation, to continue your nationwide protests in a peaceful and legal way."
Advertisement
Police on motorbikes charge protesters (Courtesy Corriere della Sera TV) - events like these are being filmed on mobile phones and uploaded online
Another defeated candidate, Mohsen Rezaie, also officially contested the results. The Guardian Council said it would rule on both complaints within 10 days.
Late on Sunday Mr Mousavi met Iran's Supreme Leader, Ayatollah Ali Khamenei, to pursue his case against the results of Friday's election.
Mr Khamanei's office said he had told the candidate that "complaints should be followed through legal channels" and urged Mr Mousavi to "follow the issue calmly".
POST-POLL CRACKDOWN
More than 100 opposition figures arrested, including the brother of ex-reformist President Khatami.
Local and international phone and text message services interrupted
Social networking and newspaper websites blocked
BBC says "heavy electronic jamming" from inside Iran disrupts its Persian TV service
International journalists arrested and asked to leave
Iranian newspapers do not carry reports of the violence
Source: Various reports
Sunday saw clashes between the police and anti-Ahmadinejad protesters in several parts of Tehran for a second day.Police hit protesters with batons and charged them on motorbikes.
Mousavi supporters cried "death to the dictator" into the evening. Scores of people are reported to have been arrested.
Mr Ahmadinejad dismissed the unrest as "passions after a soccer match".
Foreign powers have expressed concern about the election.
In an interview on US television, Vice-President Joe Biden said: "It sure looks like the way they're suppressing speech, the way they're suppressing crowds, the way in which people are being treated, that there's some real doubt."
German Foreign Minister Frank-Walter Steinmeier said he had summoned the Iranian ambassador to explain the election.
"There are a lot of reports about electoral fraud," he said.
French Foreign Minister Bernard Kouchner said: "I am sorry that instead of openness there has been a somewhat brutal reaction."
But Mr Ahmadinejad was congratulated by the presidents of Iraq, Afghanistan and Venezuela.
from twitters:
people shouting 'Mir Hossein Mousavi - President of Iran'
You may be able to watch live coverage of Iran stuff on BBC Persian.
http://www.bbc.co.uk/persian/tv/2009/01/000000_ptv_live_s.shtml
people shouting 'Mir Hossein Mousavi - President of Iran'
You may be able to watch live coverage of Iran stuff on BBC Persian.
http://www.bbc.co.uk/persian/tv/2009/01/000000_ptv_live_s.shtml
A caller from Tehran to BBC Persian mentioned Mousavi, Karoubi and if I am not mistaken Khatami are by the Sharif Univ. asking people for calm.
Plain clothes police and security forces are watching the huge crowd by the Univ. closely.
A good number of people on move from Vanak and a huge crowd on it way to Enghelab from Hafez while chanting slogans; a big number security forces (one every few meter) monitoring the crowd
Plain clothes police and security forces are watching the huge crowd by the Univ. closely.
A good number of people on move from Vanak and a huge crowd on it way to Enghelab from Hafez while chanting slogans; a big number security forces (one every few meter) monitoring the crowd
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