Iran said Thursday it had hanged 20 "terrorist" Sunni prisoners, in one of the Islamic republic's biggest mass executions in recent years.

The men, who were hanged on Tuesday, were accused of carrying out a string of attacks against civilians and religious leaders in Iran's western Kurdish region, state media reported.

Iran's intelligence ministry earlier issued a statement detailing 24 armed attacks between 2009 and 2011, including bombings and robberies, allegedly committed by the group.

It said the extremists were responsible for the deaths of 21 people in three western provinces during that time.

"102 members and followers of the... terrorist group were identified... some of whom were killed in armed clashes with police forces and some were arrested. Some of those arrested were sentenced to death while some received prison terms," it added.

One of the first plots linked to the group involved giving chocolates laced with poison to police officers and judiciary personnel, although no one was killed.

Prosecutor General Mohammad Javad Montazeri said the convicts, some of whom had come from abroad, followed "takfiri" ideologies, a term Shiite-majority Iran uses to describe Sunni jihadists.

In 2009, the group allegedly assassinated two Sunni religious leaders, Mamusta Borhan Aali and Mamusta Mohammad Sheikh al-Islam -- a provincial representative of Iran's powerful Assembly of Experts.

Those hanged on Tuesday did not deserve mercy, IRIB state television quoted Montazeri as saying.

"These people had committed murder... killed women and children, caused destruction and acted against security, and killed Sunni religious leaders in some Kurdish regions," Montazeri said.

- 977 executions in 2015 -

Iran regularly hangs large-scale drug traffickers. Murder, rape, armed robbery and adultery are also capital offences in Iran.

In addition, those charged with "spreading corruption on Earth" and "waging war against God" can be put to death under the Islamic Sharia, in force in Iran since the 1979 revolution.

According to human rights group Amnesty International, Iran was one of the world's top executioners in 2015 when it put 977 people to death, mostly on drug trafficking charges.

Amnesty does not include secretive China in its figures, but the number of executions in Iran exceeded both neighbouring Pakistan and regional rival Saudi Arabia.

Over two days in 2009, Iran hanged 44 convicted drug traffickers in one of the country's biggest mass executions.

In 2013, the Islamic republic hanged 16 Sunnis in the eastern province of Zahedan, eight of whom were members of a Sunni militant group named Jundallah, which waged a deadly insurgency on civilians and officials in southeastern Iran for almost a decade. The group's leader Abdulmalek Rigi was hanged in June 2010.

- 'Western' human rights -

Mohammad Javad Larijani, secretary general of Iran's High Council for Human Rights, said Wednesday that European Union officials have proposed talks with Iran on human rights.

He said Foreign Minister Mohammad Javad Zarif and the EU's top diplomat Federica Mogherini have already held preliminary discussions on the issue.

"We are ready to talk... but the Westerners should not put themselves forward as role models," Larijani was quoted as saying by the ISNA news agency.

"We are not happy to be executing many people, but we have a relentless war against narcotics. Poppy cultivation has increased by 40 times thanks to NATO generals in Afghanistan," he added.

Iran says claims by Western countries that they are supporting human rights -- for instance by opposing the Syrian regime of Bashar al-Assad -- have spawned greater insecurity in the region.

"Westerners defend the kind of human rights that give birth to Al-Qaeda, Daesh and terrorists," said Larijani, using the Arabic acronym for the Islamic State (IS) group.