In recent weeks, the Iranian authorities have released dozens of high-profile opposition figures who were arrested after the disputed presidential election in June, rights advocates said Friday.

The prisoners were required to post bail in the hundreds of thousands of dollars, the advocates said. Mohsen Mirdamadi, a former member of Parliament and reformist politician, was released this week after posting bail of $450,000. Saeed Leylaz, a prominent economist and journalist, and Bahman Ahmadi Amooee, another well-known journalist, were also released after paying substantial sums.

The advocacy group Human Rights Activists in Iran said Friday that about 18,000 people had been arrested since last summer, and that many of them remained in prison. Emadeddin Baghi, a human rights activist and journalist, has been in solitary confinement for the past 50 days, the opposition Jaras Web site reported. At least six people were sentenced to death last week for their role in the protests, in addition to two others who were executed in February.

On Thursday, on the eve of the Iranian New Year, the opposition leader Mir Hussein Moussavi issued a video reasserting his leadership and naming the new year one of “perseverance and patience.” It was a direct affront to Iran’s supreme leader, Ayatollah Ali Khamenei, who by tradition names the new year in a message delivered on March 21.