Activists in Iran have rejected the supreme leader's decree announcing amnesty or reduced prison sentences for thousands of people detained during anti-government protests.

According to the news agency Associated Press, this decree of the Iranian Supreme Leader Ayatollah Ali Khamenei is an acknowledgment of the detention of thousands of people in mass protests.

"Ayatollah Ali Khamenei's hypocritical apology will not change anything," said Mahmoud Amiri Magdam of the Oslo-based group Iran Human Rights.

He said that not only all the protesters should be released unconditionally, but it is also a public right that those who ordered the bloody repression and their agents should be held accountable.

Khamenei's decree came after long-detained opposition leader Mir Hossein Mousavi called for a nationwide referendum on writing a new constitution.

State media has released a list of warnings about the order, which would disqualify those with foreign ties or facing espionage charges.

State news agency IRNA said in a report in Persian that Khamenei "agreed to offer amnesty and reduce the sentences of thousands of suspects and criminals in recent incidents."

IRNA's English-language service reported that the pardons and reduced sentences were for "thousands of criminals, including those arrested in recent riots in Iran." Officials did not immediately acknowledge the discrepancy in the reports.

Reports of the decree did not provide any explanation for the decision by Khamenei, who has the final say on all matters of state in Iran.

Mir Hossein Mousavi said that he did not believe that "Iran's current system, which gives final say to a supreme leader, cannot continue."

He also called for the formation of a Constituent Assembly of 'true representatives' to draft the new constitution.

It is unlikely that Iran's theocracy will heed the 80-year-old politician's call.

He and his wife have been in detention for years since his loss in a disputed presidential election in 2009 sparked mass protests by the Green Movement.