The U.N. Commission of Inquiry on the Syrian Arab Republic published its findings Wednesday in a report based on more than 500 interviews and other evidence collected between July and January.
Paulo Sergio Pinheiro, chairman of the commission, said in a statement the level of impunity in the conflict was unacceptable. The U.N. Security Council's failure to take action to end the impunity was only making the situation worse.
"Such inaction has provided the space for the proliferation of actors in Syria, each pursuing its own agenda and contributing to the radicalization and escalation of violence," he said.
The commission's report calls on Security Council members to use their influence in Syria to persuade parties to the conflict to comply with the rules of international humanitarian law.
Civil war in Syria entered its fourth year in March. Washington and its Western allies have tried to censure Syria at the United Nations, though Russia, a permanent Security Council member with veto power, has said those efforts were biased against the government in Damascus.
British Foreign Secretary William Hague said Wednesday it was time to refer to the situation to the International Criminal Court at The Hague, Netherlands.
"We call for the situation in Syria to be referred to the International Criminal Court to ensure that the perpetrators of war crimes and crimes against humanity are held to account," he said in a statement.