Iran's judiciary announced Tuesday that 157 prisoners convicted of security offences have been pardoned as part of an amnesty granted by supreme leader Ayatollah Ali Khamenei.

In the latest amnesty, announced last week to mark the anniversary of the birth of the Prophet Mohammed, a total of 3,780 prisoners were pardoned or saw their sentences reduced, judiciary spokesman Gholamhossein Esmaili told a news conference.

Those pardoned included "157 convicted of propaganda against the state, illegal gathering, collusion against national security, or participation in the riots", Esmaili added.

The last was a reference to repeated street protests that rocked Iran between 2017 and 2019 as the economy braced for, then reeled from, sweeping sanctions imposed by the administration of outgoing US President Donald Trump.

Protests in November last year triggered by rises in the price of fuel killed 304 people, all but four of them shot dead by the security forces, London-based human rights group Amnesty International has said.

Speaking in June, a senior Iranian lawmaker put the death toll at 230 but said most were killed by armed "rioters".

Iran has released thousands of prisoners as part of measures to reduce the spread of the novel coronavirus.

But despite appeals from the United Nations and human rights groups, those convicted of security offences have generally been excluded.

In total, Iran has pardoned or granted early release to 20,000 prisoners over the past 18 months, Esmaili said.