UN investigators say Syrian leaders that they have identified as suspected war criminals should face the International Criminal Court.

The investigators urged the UN Security Council to "act urgently to ensure accountability" for violations, including murder and torture, committed by both sides in a conflict that has killed an estimated 70,000 people since a revolt against President Bashar al-Assad began in March, 2011.

“We have a permanent court, the International Criminal Court, who would be ready to take this case,” said Carla del Ponte, a former ICC chief prosecutor.

Ms del Ponte joined the UN team in September.

The inquiry, led by Brazilian Paulo Pinheiro, is tracing the chain of command to establish criminal responsibility.

"Of course we were able to identify high-level perpetrators," Ms del Ponte said, adding that these were people "in command responsibility, deciding, organising, planning and aiding and abetting the commission of crimes.”

She said it was urgent for the war crimes tribunal, based in the Hague, to take up cases of very high officials, but did not identify them, in line with the inquiry's practice.

Ms del Ponte, who brought former Yugoslav President Slobodan Milosevic to the ICC on war crimes charges, said the ICC prosecutor would need to deepen the investigation on Syria before an indictment could be prepared.

Noting that the Security Council would have to refer Syria's case to the ICC, Mr Pinheiro said: "We are in very close dialogue with all the five permanent members and with all the members of the Security Council, but we don't have the key that will open the path to cooperation inside the Security Council."

Karen Konig AbuZayd, an American member of the UN team, told Reuters it had information pointing to "people who have given instructions and are responsible for government policy, people who are in the leadership of the military, for example".

The inquiry's third list of suspects, building on lists drawn up in the past year, remains secret.

It will be entrusted to UN High Commissioner for Human Rights, Navi Pillay, upon expiry of its mandate at the end of March, the report said.

The investigators' latest report, covering the six months to mid-January, was based on 445 interviews conducted abroad with victims and witnesses, as they have not been allowed into Syria.

Government forces have carried out shelling and air strikes across Syria including Aleppo, Damascus, Deraa, Homs and Idlib, the UN report said, citing corroborating satellite images.