In this Nov. 21, 2012, file photo, an activist of India's main opposition Bharatiya Janata Party (BJP) holds a portrait of Mohammed Ajmal Kasab with a noose around his neck during celebrations of his execution, in Mumbai, India. India executed Kasab, the lone surviving gunman from the 2008 Mumbai terror attack, four years after Pakistani gunmen blazed through India's financial capital, killing 166 people and throwing relations between the nuclear-armed neighbors into a tailspin. (AP Photo/Rafiq Maqbool, File)

Baghdad - Iraq on Sunday executed 42 Sunni Muslim militants convicted on terrorism charges ranging from killing members of security forces to detonating car bombs.

The biggest mass execution this year in Iraq came after Sunni suicide attacks killed at least 60 people near the southern city of Nassiriya, a Shi'ite area, on Sept. 14, prompting Shi'ite demands for tougher judicial action.

Amnesty International criticised the move, saying on Monday that "mass execution is a shocking display of the Iraqi authorities' resort to the death penalty to try to show they are responding to security threats".

"The death penalty is an irreversible and reprehensible punishment that should not be used in any circumstances and there is no evidence to show that it deters crime more than any other means of punishment," Amnesty said in a report.

The Justice Ministry said on Sunday the 42 had been hanged at a prison in Nassiriya, three months after 14 other militants were executed following convictions for terrorism.

Islamic State claimed responsibility for three suicide attacks targeting restaurants and a security checkpoint near Nassiriya.

Relatives of victims were invited to witness Sunday's executions, the justice ministry said.

"Despite all the pain inside me after losing my two brothers in the suicide attacks, when I saw the terrorists dangling from the rope I felt relief," said Fadhil Abdul Ameer from Nassiriya.

Islamic State's self-declared caliphate, declared in 2014 after it captured wide areas of northern and western Iraq, effectively collapsed in July when U.S.-backed Iraqi forces captured Mosul, the group's de facto capital in Iraq.

But recent deadly bomb attacks in Baghdad and other cities show the jihadists remain capable of guerrilla-style warfare, a tactical shift away from seeking territorial conquest.