"The international community -- and the UN Security Council — must take the decision to refer this to justice," del Ponte, member of a UN-mandated commission of inquiry on the Syria conflict, told reporters.
"We suggest the International Criminal Court. We can't decide, but we are pressuring the international community to act, because it's time to act," she said after releasing a report by the commission on the situation in Syria after almost two years of conflict.
The commission is due next month to submit a confidential list of individuals and units allegedly involved in war crimes to the UN's Human Rights Council, but is not planning to make the list public.
Del Ponte gained renown for her tough stance as the UN's top prosecutor investigating war crimes in Rwanda and the former Yugoslavia.
"I'm not the prosecutor dealing with this case, unfortunately," she said, adding: "Justice is a contribution for peace and reconciliation."
Del Ponte, a former Swiss attorney-general, was appointed by the UN Human Rights Council to the commission investigating Syrian war crimes in September 2012.