Iraq executes a dozen of death row jihadists
Abadi, who has faced charges of failing to respond in force to IS, as well as widespread social media anger, ordered "the immediate punishment of terrorists condemned to death whose sentences have passed the decisive stage", his office said, referring to convicts whose appeals have been exhausted.
More than 300 people, including around 100 foreign women, have been condemned to death in Iraq and hundreds of others to life imprisonment for membership of IS, a judicial source said in April.
Most of the convicted women are Turkish or from former Soviet republics, while a Russian man and a Belgian national are also on death row.
Abadi vowed Thursday to avenge the deaths of the eight IS captives, a day after their bodies were found along a highway north of Baghdad.
"Our security and military forces will take forceful revenge against these terrorist cells," he told senior military officials and ministers.
"We promise that we will kill or arrest those who committed this crime," he said.
The corpses, found at Tel Sharaf in Salaheddin province, were decomposing and had been strapped with explosive vests, the army said.
They included six abductees who had appeared in an IS video with badly bruised faces. IS claimed they were Iraqi police officers or members of the Hashd al-Shaabi paramilitary force which was key to the jihadists' defeat.
In the video posted on Saturday by the Amaq propaganda outlet of IS, the militants threatened to execute their captives unless Baghdad released Sunni Muslim women held in its prisons within three days.
But Abadi said autopsies indicated the captives were already dead when the recording was posted and that "the terrorists posted the video to try to dupe us".
Iraqi security forces "will also find out who passed on information to the terrorist cell", he pledged.
Human Rights Watch last week urged Iraq's judiciary to deal with foreign women and children affiliated with IS on a case-by-case basis instead of slapping them with "one size fits all" sentences.
Since January, HRW said Iraq's judiciary had "proceeded with rushed trials against foreigners on charges of illegal entry and membership in or assistance" to the militant group.
Most foreign women had been sentenced to death or life in prison and children aged nine and above to between five and 15 years in jail for taking part in violent acts, it said.
The New York-based watchdog called on Iraq "to take into account their individual circumstances and actions and give priority to prosecuting the most serious crimes while exploring alternatives for lesser ones".