GENEVA (AP) — The deaths of up to 500 migrants and refugees in an intentional boat-ramming in the Mediterranean Sea last week could be an act of mass murder, the U.N. rights chief said Friday, calling for nations to properly investigate the incident.

Up to 500 Syrians, Palestinians, Egyptians and Sudanese migrant workers and refugees were aboard the boat that left from the Egyptian port of Damietta and are feared dead at the hands of human traffickers who rammed and sank the boat off the Malta coast.