All sides in the Syrian civil war have committed crimes against humanity, since the conflict began five years ago, a U.N.-backed panel said Monday at the release of its latest report.

"Flagrant violations of human rights and international humanitarian law continue unabated, aggravated by blatant impunity," the U.N. Independent International Commission of Inquiry said in its 31-page findings.

OPINION: War Is Still Not the Answer

"The stipulations of relevant Security Council resolutions ... remain largely unheeded and unimplemented," it reported, adding "war crimes are rampant," on both sides

The U.N. inquiry, composed of independent experts, has long denounced the use of starvation in the Syrian conflict as a weapon of war.

"Government forces, anti-government armed groups and terrorist organizations employ sieges and consequent starvation, denial of humanitarian access and other forms of deprivation as instruments of war to force surrender or to extract political concessions," it said.

The commission's chairman, Paulo Pinheiro, told reporters at U.N. headquarters that no warring party respects international humanitarian law.

The commission urged the 15-nation Security Council to refer the conflict in Syria to the International Criminal Court in The Hague.