LONDON - The United Nations human rights chief said on Saturday Syrian President Bashar al-Assad should be probed for war crimes and called for immediate action by the international community, including possible military intervention.

Navi Pillay, the UN high commissioner for human rights, repeated her call for the Syrian president to be referred to the International Criminal Court for the actions of his forces in the civil war which the UN says has left almost 70,000 dead in 22 months of fighting.

Asked if Assad should be investigated for war crimes, she told Britain's Channel 4 News: "He's not but he should be.

"This is my strong call that I made 18 months ago. Based on the evidence, I said crimes against humanity and Syria's war crimes are being committed by President Assad's forces, his security forces, and other groups allied to him," she said.

"There should be a referral by the Security Council to the International Criminal Court. I would describe (Assad's actions) as evidence of crimes against humanity and war crimes, against his own people."

World powers are divided on how to stop the escalating violence in Syria and the Security Council is unlikely to refer the matter to the International Criminal Court in The Hague, which is not an official UN body.

Pillay said the Security Council had a range of tools to keep warring sides apart to allow negotiations, and said action was needed urgently.

"I'm not arguing for any specific intervention," she said. "It's an intergovernmental decision on what kind of action - intervention, peacekeeping, military intervention or a referral to the International Criminal Court. We urge that action be taken immediately. "

However, she acknowledged that after the UN intervention in Libya in 2011 which led to the ousting of former leader Muammar Gaddafi, some members of the Security Council were loathe to use force again, in case it led to regime change and "so acting out the interests of one or other government".

"This is what I'm hearing in the Security Council," she said.

"If there is doubt and hesitation it is because people are assessing the value of military intervention in places like Libya, Syria and Afghanistan. That it could become a long, drawn out war with no guarantees that civilians will not be harmed in that process."