"France is opposed in principle to the death penalty at all times and in all places," the foreign ministry said in a statement after the three IS members were sentenced on Sunday.

It said the detained men were receiving consular assistance to ensure they had legal representation ahead of an expected appeal of the ruling, which they can lodge within 30 days.

It added, however, that France "respects the sovereignty of Iraq's institutions".

France has long insisted that its adult citizens captured in Iraq or Syria must face trial locally, refusing to repatriate them despite the risk they face capital punishment for waging their jihadist war in the region.

The three French fighters, Kevin Gonot, Leonard Lopez and Salim Machou, were transferred to Iraq for trial after being caught by US-backed forces in Syria.

They were among 13 French nationals caught in battle-scarred eastern Syria and handed to Iraqi authorities in February on suspicion of being members of IS's feared contingent of foreign fighters.

Iraq has taken custody of thousands of jihadists, and the Iraqi judiciary said recently that it had tried and sentenced more than 500 suspected foreign members of IS since the start of 2018.

Its courts have condemned many to life in prison and others to death, though no foreign IS members have yet been executed.