A UN envoy has said more than 50 mass graves have so far been found in parts of Iraq that were previously controlled by so-called Islamic State (IS).

Jan Kubis told the UN Security Council that it was "evidence of the heinous crimes" IS had committed.

The graves have been discovered in recent months as territory has been re-captured from IS.

Most recently, graves found in the city of Ramadi in April may contain the remains of up to 40 people.

Mr Kubis said the international community should "take steps to ensure the accountability" of IS fighters.