GENEVA — Syrian President Bashar Assad's forces and pro-government shabiha fighters have perpetrated war crimes and crimes against humanity on Syrian civilians, a U.N. expert panel concluded Wednesday in a report that provides in chilling detail further evidence of a conflict spiraling out of control.

The panel appointed by the U.N.'s 47-nation Human Rights Council blamed the government and allied militia for the killing of more than 100 civilians in the village of Houla in May, nearly half of them children, and said the murders, unlawful killing, torture, sexual violence and indiscriminate attacks "indicate the involvement at the highest levels of the armed and security forces and the government."

The panel also concluded in its final report Wednesday to the Geneva-based council that anti-government armed groups committed war crimes, including murder, extrajudicial killings and torture, but at a lesser frequency and scale.