At least 833 children of 14 nationalities are currently in prison in Iraq, according to the Joint Operations Command, which coordinates the fight against the Islamic State group.

"We ask all diplomatic missions in Iraq, resident and non-resident, to take back their nationals who have served their sentences and children who are not convicted," said foreign ministry spokesman Ahmed Mahjoub.

"Iraq has informed all of the countries that have citizens in its prisons. We have already spoken with the embassies of Germany, Azerbaijan, Russia and other countries to take (their citizens) back."

Iraqi law renders children punishable at the age of nine, according to Human Rights Watch.

They face five years in prison for belonging to IS, which swept across Iraq in 2014 and controlled large swathes of the country until last year.

Under Iraqi law, children can face up to 15 years in prison for violent acts.

A Russian diplomatic source in Moscow told AFP that there "are 70 Russian women on trial and there are about 100 children in Iraqi prisons".

"We are trying to bring these children back to Russia after identifying them because almost all of them do not have identity papers," the source said.