The United Nations expressed profound concern on Saturday over reports of an incident in the battle for the Iraqi city of Mosul that caused a high number of civilian casualties.

"We are stunned by this terrible loss of life," Lise Grande, the humanitarian coordinator for Iraq, said in a statement.

Local officials and residents said on Thursday that dozens of people were buried in collapsed buildings after an air raid against Islamic State militants in the al-Aghawat al-Jadidah district triggered a huge explosion last week.