At least 300 people, including around 100 foreign women, are on death row in Iraq and hundreds bagged life imprisonment.

Iraqi Prime Minister Haider al-Abadi on Thursday ordered the immediate execution of all convicted “terrorists” of the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group, on death row, in swift retaliation for the group’s execution of eight captives.

Abadi “ordered the immediate execution of terrorists condemned to death whose sentences have passed the decisive stage,” his office said, referring to convicts whose appeals have been exhausted.

He had vowed to avenge the deaths of ISIL captives, a day after their bodies were found along a highway north of the capital, 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 on Wednesday 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 ISIL video with badly bruised faces.

ISIL claimed they were Iraqi police officers or members of the Hashed al-Shaabi paramilitary force.

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 the ISIL group, a judicial source said in April.

Most of the convicted women are from former Soviet republics, while a Russian man and a Belgian national are also on death row.

Iraq declared victory over ISIL in December after expelling the fighters from all urban centres including second city Mosul in a vast military campaign.

But the Iraqi military has kept up operations targeting mostly desert areas along the porous border with Syria.