Traces of explosives have been found on the bodies of some victims of the EgyptAir flight that crashed into the Mediterranean in May, Egyptian authorities said Thursday, raising new concerns that the crash was the result of an act of terrorism.

EgyptAir flight 804 went down as it flew from Paris to Cairo, killing all 66 people onboard. No terrorist group claimed responsibility for downing the airliner and investigators from France and Egypt have not determined the cause of the crash.

The Egyptian investigating committee said in a statement that “traces of explosive materials” had been found on human remains and that a criminal investigation had been automatically opened in response to the findings.