Authorities in Iran have executed three men sentenced to death in connection with the nationwide anti-government protests last year, the judiciary says.

The three were convicted over their alleged involvement in a shooting attack that killed three security personnel in Isfahan in November.

Amnesty International says they were subjected to unfair trials and allegedly tortured.

Four other protesters have been hanged since December.

Dozens more have reportedly been sentenced to death or charged with capital offences.

The protests swept across the Islamic Republic following the death in custody of Mahsa Amini, a 22-year-old Kurdish woman who was detained by morality police in Tehran in September for allegedly wearing her hijab "improperly".

The three who were executed on Friday - Majid Kazemi, 30, Saleh Mirhashemi, 36, and Saeed Yaqoubi, 37 - were arrested after protests in the central city of Isfahan on 16 November, during which two Basij paramilitary force members and a police officer were shot dead.

Sources told Amnesty International that the men were forcibly disappeared, then tortured and forced to make incriminating statements that formed the basis of the criminal cases against them.

Interrogators allegedly suspended Kazemi upside down, showed him a video of them torturing his brother, subjected him to mock executions and threatened to kill his brothers.

In an audio message from inside Dastgerd prison, where the three men were held, Kazemi was heard saying: "I swear to God I am innocent. I didn't have any weapons on me. They [security forces] kept beating me and ordering me to say this weapon is mine.

"I told them I would say whatever they wanted, just please leave my family alone."

A Revolutionary Court convicted Kazemi and the other two men of "enmity against God", a vaguely-defined national security charge, and sentenced them to death in January following what activists said was a four-day trial.

According to the US-based Center for Human Rights in Iran (CHRI), they were denied the ability to prepare a proper defence, prosecutors relied on forced "confessions" and the indictment was "riddled with irregularities that reveal this was a politically motivated case".

Last week, authorities announced that the supreme court had upheld their sentences.

"The use of the death penalty against these men is a blatant act of vengeance against a courageous generation of protesters for steadfastly demanding the rights of Iranian people during the past seven months," Diana Eltahawy, Amnesty's Middle East deputy director, said in a statement on Wednesday.

"The shocking manner in which the trial and sentencing of these protesters was fast-tracked through Iran's judicial system amid the use of torture-tainted 'confessions', serious procedural flaws, and a lack of evidence, is another example of the Iranian authorities' brazen disregard for the rights to life and fair trial."

UN human rights chief Volker Türk last week expressed dismay at what he called the "frighteningly high number of executions" this year in Iran.

He cited the UN's sources as saying that at least 209 people had been put to death so far this year - more than 10 people each week - mostly for drug-related offences, calling it "an abominable record".