Evidence has been uncovered in Syria that implicates President Bashar al-Assad and members of his entourage, in war crimes and crimes against humanity, UN human rights chief Navi Pillay said Monday

A UN commission of inquiry into human rights violations in Syria "has produced massive evidence ... (of) very serious crimes, war crimes, crimes against humanity," she said, adding that "the evidence indicates responsibility at the highest level of government, including the head of state."

The commission, tasked with probing rights violations in Syria since shortly after the conflict erupted in March 2011, has repeatedly accused the Syrian regime of crimes against humanity and war crimes.

It has said the rebels fighting Assad's regime are also guilty of war crimes.

But the four-member team, headed by Brazilian Paulo Sergio Pinheiro and including former war crimes prosecutor Carla del Ponte, has never named names nor pointed directly at Assad.

The investigators -- who without access to Syria have relied on more than 2,000 interviews in the surrounding region or by phone or Skype for their reports -- have put together a long list of suspected perpetrators.

The names "remain sealed until I am requested to furnish them to credible investigation," Pillay told reporters in Geneva, adding that "it could be a national investigation or international investigation."

She meanwhile reiterated her call for the case to be handed over to the International Criminal Court in the Hague to ensure accountability.

"The scale of viciousness of the abuses being perpetrated by elements on both sides almost defies belief," she said.