"I do not know the answer to that question," Kirby said, when asked whether US-supplied weapons or resources were involved in the strike.
Ben Saul, the UN special rapporteur on human rights and counter-terrorism, has since said that the bombing may constitute a violation of international humanitarian law and a war crime.
Following the incident, Israeli Prime Minister Benjamin Netanyahu has come under pressure from his allies over the country's airstrike on the urgently needed convoy.