Iran's top reform leaders threatened Sunday to walk out of government if hard-liners continue thwarting President Mohammad Khatami's political and social reforms.

"We would not hesitate for a moment to quit the establishment if we lose all hope of carrying out the demands for which people voted," said Mohammad Reza Khatami, leader of Iran's largest reformist party, the Islamic Iran Participation Front.

Khatami, the president's younger brother and parliament's vice speaker, said continued judiciary blocking of freedom of expression will either "lead to total chaos or a black dictatorship in Iran."

He cited a death sentence issued against Hashem Aghajari, a university professor accused of insulting Islam and questioning hard-line clerics, and the detention of several key reformers.

"Illogical judiciary actions have harmed Iran's image and dashed hopes at home for reforms. But public protests against them have revived some hopes of withstanding pressure and pushing for reforms ...," Khatami said.

Aghajari's case has highlighted the tense power struggle between reformists supporting President Khatami's reform programs and hard-liners who control unelected institutions, including the police, judiciary and other key levers of power.

Last week, after weeks of student protests, Iran's supreme leader Ayatollah Ali Khamenei ordered a review of Aghajari's death sentence. The judiciary has moved slowly on the ordered review.