The group, which the US military transferred to Iraq on Wednesday, were "all leaders of the Islamic State group, and some of the most notorious criminals," and included "Europeans, Asians, Arabs and Iraqis," one security official said.

Another security source said the group included "85 Iraqis and 65 others of various nationalities, including Europeans, Sudanese, Somalis, and people from the Caucasus region".

He added that they "all participated in IS operations in Iraq," including the 2014 offensive that saw the jihadist group seize large areas of Iraq and neighbouring Syria.

"They are all at the level of emirs," the official added.

They are now held at a prison in Baghdad.

The group is the first batch of 7,000 IS suspects, previously held by Syrian Kurdish fighters, that the US military said it will transfer to prisons in Iraq.

Thousands of suspected jihadists and their families, including foreigners, have been held in detention centres and camps in Syria since IS's defeat in 2019 at the hands of Kurdish-led forces backed by a US-led coalition.

Washington announced the plan to transfer IS detainees after the Kurdish-led forces relinquished swathes of territory under pressure from Syrian government forces.

The Iraqi judiciary said it would launch legal proceedings against the IS detainees transferred from Syria.

Iraqi courts have handed down hundreds of death sentences and life prison terms to people convicted of terrorism offences, including hundreds of foreign fighters -- some caught in Syria and transferred across the border.