The U.N. commission investigating war crimes in Syria says President Bashar Assad's government is committing the bulk of atrocities inside the war-torn country, exceeding the toll from the horrific massacres perpetrated by Islamic State fighters.

The head of the U.N. commission, Brazilian diplomat and scholar Paulo Sergio Pinheiro, describes the Islamic State extremist group and anti-government armed groups capturing the world's attention as "agents of death and destruction," but emphasizes the government's sieges and attacks in Syria's civil war which has killed over 190,000 people and destabilized the region.

He told the 47-nation U.N. Human Rights Council in Geneva on Tuesday "the Syrian government remains responsible for the majority of the civilian casualties, killing and maiming scores of civilians daily" through shelling, air attacks, checkpoints and interrogation.