France on Monday confirmed that an Iraqi court that sentenced four French citizens to death as members of Islamic State of Iraq and the Levant had jurisdiction to do so but said it would take "the necessary steps" to try to prevent them from being executed.

Three French fighters were handed the death penalty on Sunday. Kevin Gonot, Leonard Lopez and Salim Machou, had been transferred to Iraq after being caught by US-backed forces in Syria.

The court sentenced a fourth French national, Mustapha Merzoughi, 37, to death by hanging on Monday.

The men were among 13 French nationals caught in eastern Syria and handed to Iraqi authorities in February on suspicion of being foreign fighters for Isil. Others were due to be sentenced.

France has long insisted that its adult citizens captured in Iraq or Syria must face trial locally, refusing to repatriate them despite the risk of them receiving death sentences.

On Monday, France’s foreign ministry said that Isil “terrorists must answer for their crimes in court”.

Adults detained in Iraq must be tried by the Iraqi justice system, as soon as it declares itself competent. France, it said, "respects the sovereignty of Iraq's institutions".