The United Nations human rights chief has accused the so-called Islamic State group of murdering 163 civilians to prevent them from fleeing Iraq's western Mosul last week.

Zeid Ra'ad Al Hussein told the opening of the UN Human Rights Council that his staff had reported that "bodies of murdered Iraqi men, women and children still lay on the streets of the al-Shira neighbourhood of western Mosul, after at least 163 people were shot and killed by Daesh to prevent them from fleeing.

His spokesman Rupert Colville told AFP that the killings were believed to have taken place on 1 June.

Daesh is an Arabic acronym for IS.

IS seized Mosul in 2014, and the operation that began last October to retake the city has pushed hundreds of thousands of residents to flee their homes.

Iraqi forces have retaken all but a handful of areas around the Old City in western Mosul, but the jihadists are fighting in densely populated areas, and have used civilians as human shields at various points in the battle.

The United Nations warned at the end of May that up to 200,000 civilians may still be trapped in IS-held areas, facing shortages of food, water and medicine as well as deadly danger from the battle for the city.

Mr Zeid condemned "in the strongest terms the cowardly and sickening attacks perpetrated against innocent people by callous terrorists operating in many parts of the world."