UN Secretary-General Antonio Guterres has said that a UN commission investigating war crimes in Syria should continue its work despite the resignation of a prominent member of the panel in protest.

Commissioner Carla del Ponte, a former war crimes prosecutor, announced she was quitting on August 6, saying that the commission "simply doesn't do anything" despite grave injustices occurring in Syria.

"The terrible crimes committed in Syria I neither saw in Rwanda nor ex-Yugoslavia," Del Ponte told the Swiss newspaper Blick.

UN spokesman Stephane Dujarric told reporters in New York that Guterres regretted her decision to resign but believed the commission will remain "an important and integral part of the accountability process."

The commission has repeatedly urged the UN Security Council to ask the International Criminal Court to open an investigation into war crimes in Syria.

But an effort by the council in 2014 to refer Syria to The Hague court was blocked by China and Russia, Syria's ally.

Frustrated by the Security Council's inaction on Syria, the UN General Assembly last year set up an international panel to help collect evidence to be used in future cases of war crimes prosecution.

Based on reporting by AP and AFP