Instead, the Baghdad court said, their interrogations had found the unnamed Frenchman travelled to Syria "in support of the Yazidi cause".

In February, the US-led coalition fighting the Islamic State group handed to Iraqi authorities 13 French nationals caught in IS's dwindling "caliphate" in east Syria.

All 13 were thought to be members of IS's feared contingent of foreign fighters, and Iraqi President Barham Saleh pledged they would be tried "according to Iraqi law".

But as Iraqi prosecutors began investigating, "terrorism" cases were only prepared against 12 nationals.

On Thursday, the Karkh Special Investigations Court for Terrorism Issues in Baghdad announced it "let go one of the 13 accused French nationals due to a lack of evidence".

After months of investigations, the court said, "there was no proof of his involvement in any military activities, and his entry (to Syria) was in support of the Yazidi cause".

During IS's rampage across northern Iraq in 2014, it slaughtered thousands of members of the Yazidi community and seized its women and girls as sex slaves.

The atrocities prompted the US-led coalition to begin a military intervention against IS in Iraq, which it then expanded into Syria by backing a Kurdish-led fighting force.

That force, the Syrian Democratic Forces, attracted hundreds of foreign fighters who wanted to join the fight against IS.

The court found that the French national entered Syria "legally," but did not say which border crossing he used or what exactly he was doing there.

It also remains unclear why the SDF or the US-led coalition handed him over to Iraqi authorities along with suspected jihadists if he had been supporting Yazidis, which would have put him on the other side of the front line against IS.

With the collapse of IS's self-styled "caliphate" last month, dozens of kidnapped Yazidi women and children have been freed.