Evidence collected by UN investigators examining Syrian war crimes implicates President Bashar al-Assad, United Nations human rights chief Navi Pillay said.

Ms Pillay later denied having direct knowledge of their secret list of suspects.

However, her remarks about the head of state were at odds with a policy of keeping the identity of alleged perpetrators under wraps pending any judicial process.

The UN investigators collect testimony in utmost secrecy and independently from Ms Pillay.

They have previously said the evidence points to the highest levels of Syria's government, but have not named Mr Assad or any other officials publicly.

They have compiled secret lists of suspects and handed them to Ms Pillay for safe storage.

The hope is that one day suspects will face trial for violations, including torture and mass killings.

"They point to the fact that the evidence indicates responsibility at the highest level of government, including the head of state," Ms Pillay told a news conference.

But Ms Pillay said even she cannot unseal the confidential lists, and insisted she was only repeating what the investigators led by Brazilian expert Paulo Pinheiro had said.

World powers should make accountability for crimes committed in the civil war a priority ahead of Syrian peace talks set for 22 January, she added.

The UN estimates that more than 100,000 people have been killed in the conflict.

The question of whether Mr Assad can remain in power after the fighting stops has been one of the major areas of disagreement between the US and Russia, the two main sponsors of the peace talks. 

Ms Pillay and Mr Pinheiro have repeatedly called for Syria to be referred to the International Criminal Court, a move that could lead to the prosecution of suspects on the secret list.