As part of a broad crackdown on the media and perceived dissidents, the Iranian government has arrested 23 journalists and bloggers since the disputed presidential election on June 12.
A spokesman for Mousavi said today more than 700 supporters and organizers have also been detained over the past week, among them former Vice President Mohammed Ali Abtahi and Ebrahim Yazdi, a former foreign minister and architect of the Islamic Recpublic.
The official death toll in the often violent clashes between police and demostrators is 17, but many observers have suggested that the true count is much higher.
Iranian state television today announced the arrest of Faezeh Hashemi Rafsanjani and four other family members of a powerful former president, Ali Akbar Hashemi Rafsanjani.
Also today, Newsweek Magazine announced the arrest of staff reporter Maziar Bahari, a Canadian national who has lived in Iran and reported on the country for the past decade. Newsweek issued a statement saying Bahari was held without charge.
"Newsweek asks that world governments use whatever influence they have with the governemnt in Tehran to make clear that this detention is unwarranted and unacceptable, and to demand Mr. Bahari's release," the statement said.
Ali Mazroui, head of the Association of Iranian Journalists, was also arrested this morning.
Also among the detainees is journalist and women's rights advocate Jila Baniyaghoob. According to the non-governmental organization Reporters Without Borders, she and her husband, journalist Bahaman Ahamadi Amoee, were arrested by plainclothes intelligence forces at midnight on June 20.
Baniyaghoob is a winner of the Courage in Journalism award of the International Women's Media Foundation. She has spent a large portion of career advocating for women's rights in Iran and throughout the Middle East.
Before her detention, she was editor-in-chief of the online newspaper Kanoon Zanon Irani, literally "Focus on Iranian Women."
Throughout the unrest set off by the disputed election, Iran has restricted foreign journalists from covering opposition protests on the ground. ABC News cameras were seized last week.
The Tehran offices of Al Arabiya, a Saudi-owned network based in Dubai, were suspended until further notice.
In 2008, Iran was ranked number 166 out of 173 countries in press freedom index compiled by Reporters Without Borders. The organization described journalism in Iran as "a high risk exercise involving endless frustration and constant police and judicial harassment."
Confrontations were reported in the Iranian cities of Tehran, Shiraz, Esfahan and Rasht, as riot police and members of a religious militia known as the Basij cracked down on protests declared illegal by the state. They were chronicled by street-level observers and echoed around a world watching online.
Early Sunday, supporters of Mir Hossein Mousavi, whose alleged presidential election defeat a week ago touched off the protests, told ABC News they were planning new protests and hoping to shut down Tehran's main market, known as the bazaar.
State television has referred to the protesters as "terrorists," and allowed little information about the rallies to reach domestic viewers.
"It feels like a bad movie, as though everyone is pretending that yesterday did not happen," said one person in Tehran in an e-mail to ABC News.