US illegally transferring Islamic State suspects from Syria to Iraq for trial: HRW

US forces have been handing over suspected members of the Islamic State (IS) group captured in Syria to authorities in Iraq, where they face torture and botched trials, Human Rights Watch (HRW) has said.

The New York-based organisation said on Thursday that the United States had transferred suspected members of IS for trials in Baghdad, some of which had already taken place.

"Prosecuting [IS] suspects is crucial for their countless victims to obtain justice, but that won't be achieved by transferring detainees to abusive situations," HRW's Nadim Houry said.

"The US should not be transferring IS suspects from Syria to Iraq or elsewhere if they will be at risk of torture or an unfair trial."

International human rights and humanitarian law prohibits the transfer of detainees to countries where they are at serious risk of torture and mistreatment, the organisation said.

HRW said independent observers of four recent terrorism trials in Baghdad reported that several foreign defendants, including from France, Australia, and Lebanon, had been tried in Iraq based, at least in part, on their alleged membership of IS.

The defendants reported their capture in and transfer from Syria during the trials.

Some alleged due process violations and, in two cases, being tortured in Iraq, the organisation said.

A fifth detainee, a Palestinian national from Gaza, was also transferred from northeast Syria into Iraqi custody but HRW said it did not know if he had been charged in Iraq.

Controversial subject

In some cases, the defendants said they had never been to Iraq before.

"Faced with the refusal by many countries to take back their nationals, the US seems to have taken the easy way out by transferring some to Iraq and be done with it," Houry said.

"The US needs to create a system that won't make the US complicit in torture and ensures that [IS] suspects are fairly tried for their crimes, however heinous."

An independent source monitoring events on the border between Iraq and Syria told HRW that it was aware of "many" US transfers of foreign IS suspects from Syria to Iraq but was unable to quantify them.

Faced with the refusal by many countries to take back their nationals, the US seems to have taken the easy way out by transferring some to Iraq and be done with it

- Nadim Houry, HRW

HRW said it had reason to believe that in at least five instances, US forces handed foreign detainees over to Iraq's Counter Terrorism Service.

The organisation said the US government had yet to respond to its letter from 10 September, seeking clarification about US policy on the transfer of detainees held in northern Syria, including the number transferred to Iraq.

The fate of hundreds of foreign suspected IS members detained by Kurdish forces in the semi-autonomous northeastern region of Syria has become a controversial subject.

Most of their governments have refused to repatriate them for trials at home and the Kurdish administration holding them has signalled that it does not intend to try them locally.

In June, it was revealed that a US-Saudi man suspected of being an IS member was set to be released in an unknown Syrian town or displacement camp rather than be tried in the United States or Saudi Arabia.

His lawyer described it as a "death warrant".