"Andisheh No (New Thought) newspaper run by Hojatollah Hajebi was banned today by the press watchdog board," Fars news agency said referring to the paper's managing director.
The newspaper's public relations service told AFP they were unaware of the ban.
The ISNA news agency reported that the closure was due to "numerous violations" and came after "several notices by the press watchdog."
The violations included "questioning general policies of the Islamic republic with regard to empowering the oppressed nations of the world" and "a constant effort to deepen differences among people after the presidential election," ISNA said.
It did not elaborate further but the Islamic regime is a fervent supporter of the Palestinian cause and most notably Hamas militants.
Iran's ILNA news agency, which is close to reformists, has also received "notice" from the culture and Islamic guidance ministry which supervises media, the website of parliamentary reformist faction, Parlemannews.ir, said.
"In order to prevent divisions and other similar incidents the ministry has asked ILNA to avoid producing and covering news which is particularly related to the Green Movement," the report said.
It said that the ministry was not "satisfied with the agency's performance."
Iran's opposition supporters who have rejected the re-election of President Mahmoud Ahmadinejad as fraudulent are known as the "Green Movement."
The government has stepped up pressure on pro-opposition media and Andisheh No was the second reformist paper shut down in December.
Earlier this month Iran shut down Hayat-e No (New Life), a newspaper which belonged to supreme leader Ayatollah Ali Khamenei's brother, Hadi Khamenei, an outspoken critic of Ahmadinejad.
The hardline press watchdog has also warned several reformist newspapers over their coverage of Iranian politics.
Ahmadinejad's disputed June 12 re-election has bitterly divided Iran's political elite amid persistent allegations the poll was massively rigged in his favour.
His government has cracked down on critical media mostly belonging to the rival reformist camp but conservative media have also been hit by a number of closures.
