Foreign media have been banned from covering street protests since the demonstrations over the disputed June presidential vote, which the opposition says was rigged to secure President Mahmoud Ahmadinejad's re-election.
"Farhad Pouladi was covering the rally when he was stopped and taken away by three security agents, two in uniform and one in plainclothes," acting Tehran bureau chief Jay Deshmukh said.
"Since yesterday morning, we have no news about him."
Police clashed with supporters of Iran's opposition leader Mirhossein Mousavi in Tehran during the annual anti-U.S. rally.
Deshmukh said the Ministry of Culture and Islamic Guidance had given assurances to AFP that Pouladi's case was being followed as a priority.
The reformist Mowjcamp website said at least 23 people were arrested in Tehran and the northern city of Rasht during the protests.
(Writing by Parisa Hafezi; editing by Alison Williams)
