Some of the children are foreigners whose parents brought them to be raised under Islamic State rule, or child fighters conscripted into what the group dubbed "cubs of the caliphate."

Eleven children are among 26 Syrian civilians killed by Russian air strikes on Islamic State territory in the southwestern province of Daraa, according to the Syrian Observatory for Human Rights. 

The White House said Russian aircraft flew bombing missions in defiance of a United Nations ceasefire.

Russian news reports said an unknown number of Russian military contractors were killed in a U.S. counterattack last week.

The top UN human rights official said the violence may constitute war crimes.