Iran's supreme leader has announced pardons for a significant number of prisoners, including those arrested in recent anti-government protests.

Ayatollah Ali Khamenei made the announcement on Sunday ahead of the 44th anniversary of the country's Islamic Revolution on February 11.

Khamenei agreed to offer amnesty and reduced sentences to what authorities say are "tens of thousands" of detainees, including participants in the demonstrations.

Nationwide protests erupted in September after a woman died in police custody. She had been arrested for allegedly not wearing her headscarf properly.

Iranian authorities have yet to say how many of those detained in the protests will be subject to the amnesty and sentence reductions.

They say the pardons would apply to those who have not conducted direct communication with agents of foreign intelligence services, have not committed intentional murders or injuries, and have not destroyed public facilities, among other acts.

The Norway-based group Iran Human Rights wrote on Twitter that the "hypocritical amnesty" of protesters by Ali Khamenei is a propaganda measure.

The country's handing down of death sentences for participants in the anti-government protests caused uproars within and outside Iran. But the street protests in Iran have now almost settled down.