The United Nations Human Rights council estimates 10,000 to 15,000 people have been killed on both sides in four months of fighting in Libya.
A panel sent by the council visited Tripoli and rebel-held areas in late April.
It reports finding evidence of war crimes by forces of the Libyan leader, Muammar Gaddafi, including attacks on civilians, aid workers, and medical units.
It also found some evidence of crimes by opposition forces.
Libya has denied the charges and accused rebels of butchery and cannibalism.