Iran's police arrested Monday some opponents as well as several aides to main opposition leaders after eight people died in fierce clashes in Tehran, websites said.
Jaras said opposition politician Ebrahim Yazdi, leader of the banned Freedom Movement and foreign minister in Iran's first government after the 1979 Islamic revolution that overthrew the U.S.-backed shah, was detained early on Monday at his home.
Jaras opposition website said three advisers of Mousavi were detained on Monday, a day after five people were killed in Tehran. Earlier the website reported the arrests of four pro-reform politicians.
The Intelligence Ministry said members of an exiled opposition group, the Mujahideen Khalq Organisation, were among those arrested.
Opposition website Rahesabz said that Ebrahim Yazdi, who served as foreign minister in the early months of the 1979 Islamic revolution, and award-winning rights campaigner and journalist Emadeddin Baghi, were both arrested Monday.
Parlemannews said Iranian authorities had also rounded up several aides to reformist ex-president Mohammad Khatami and opposition leader Mir Hossein Mousavi.
Parlemannews named the Khatami aides arrested as Morteza Haji and Hasan Rasoolid and said they run his non-governmental Baran organisation.
"Mousavi advisors Alireza Beheshti, (Ghorban) Behzadian-Nejad and (Mohammad) Bagherian were also arrested in the morning," the website added.
Police fired teargas on Monday to disperse supporters of opposisiton Mirhossein Mousavi who gathered to express their condolences over his nephew's death in an anti-government rally, an Iranian opposition website said.
"A group of Mousavi supporters have gathered in front of Ebn- e Sina hospital where his nephew's body was kept ... Police fired teargas to disperse them," the Norooz website reported.
Iran's Supreme National Security Council said eight people were killed on Sunday in anti-government protests across Iran that erupted during the religious festival of Ashura. Iran's Health Ministry said over 60 people had been injured in Tehran.
Among the dead on Sunday was a nephew of Mousavi. State television said unknown assailants killed Ali Habibi Mousavi Khamene. A Mousavi ally described his death as martyrdom.
A website said on Monday the body of Mousavi's nephew was missing from the hospital.
"We can not hold a funeral until my brother's body is found," said another of Mousavi's nephews said, according to parlemannews.
Police said the "suspicious deaths" were under investigation and that 300 protesters had been arrested, adding dozens of security men had been injured in the running street clashes.
Jaras said police shot dead four protesters in central Tehran on Sunday and that unrest had also erupted in the cities of Qom, Shiraz, Isfahan, Najafabad, Mashhad and Babol.
Tabriz prosecutor Yahya Mirzamohammadi denied a Jaras report that four protesters had been killed in the northwestern city. He told the ISNA news agency no protests had occurred there.
A clerical group in the holy city of Qom condemned the "sedition by rioters" during the Shi'ite Muslim religious ritual of Ashura, the official IRNA news agency said.
"The association of Qom theologians ... asks officials to identify those behind yesterday's events and take appropriate measures to firmly encounter and punish them according to legal and religious standards," it said in a statement.
The United States condemned Iran's "unjust suppression" of civilians and said it "sided" with protesters.
The reports could not be independently verified because foreign media are banned from directly covering protests.