By Parisa Hafezi
"The pro-reform path will continue," Mousavi said in a statement. "The establishment should respect the constitution and let us to gather to commemorate our killed loved ones on Thursday."
Moderate defeated candidates Mousavi and Mehdi Karoubi on Sunday called on the authorities to permit a gathering on Thursday at Tehran's "Grand Mosala," a prayer location where tens of thousands can gather, to commemorate unrest victims.
The June 12 vote plunged the country into its biggest internal crisis since the 1979 Islamic revolution and exposed deepening divisions in its ruling elite.
Iranian media have reported several cases of protesters' deaths following the vote, including those of Sohrab Aarabi and Mohsen Ruholamini.
Rights groups say hundreds of people, including senior pro- reform politicians, journalists, activists and lawyers, have been detained in Iran since the election, which moderates say was rigged in favor of hardline President Mahmoud Ahmadinejad.
Mousavi, prime-minister in 1980s, said detentions could not halt the pro-reform movement.
"The killings and arrests are a catastrophe, people will not forgive those behind such crimes," Mousavi said, adding: "I am sure the judiciary is not informed about many arrests."
"The country of 70 million cannot become a prison for all of them. The more they arrest people, the bigger this movement becomes."
Iran's top judge Ayatollah Mahmoud Hashemi-Shahroudi ordered the judiciary on Monday to follow the cases of detained protesters, the students news agency ISNA quoted judiciary spokesman as saying.
Challenging the authority of Iran's most powerful figure Supreme Leader Ayatollah Ali Khamenei, who has endorsed the re- election of the president, Mousavi said the vote result would damage the clerical establishment.
"People made the (1979 Islamic) revolution for freedom. Where is that freedom now? This situation will destroy everyone and will harm the system," Mousavi said.
(Writing by Parisa Hafezi; Editing by Samia Nakhoul)
