United Nations Secretary-General António Guterres condemned the carnage at a food aid site in Gaza, where the strip's health ministry said more than 100 people were killed.

Israeli forces opened fire as scores of people were waiting for food, according to the Palestinian health ministry in Gaza. Israel's military and eyewitnesses have provided contradictory accounts of the events on the ground.

"The desperate civilians in Gaza need urgent help, including those in the besieged north where the United Nations has not been able to deliver aid in more than a week," Stéphane Dujarric, spokesperson for the UN chief, said in a statement.

The UN was not present during the incident but called for an investigation, Dujarric said. Guterres said later Thursday the deaths would require an effective, independent investigation.

Israel Defense Forces spokesperson Lt. Col. Peter Lerner told CNN the aid trucks involved in Thursday's deadly incidents were from "international aid by governments that came on in private truckloads to move north."

"We need to do everything in order to alleviate the humanitarian situation," he said.

Guterres said he is also "appalled" by the number of Gazans killed in the war. The health ministry in the strip announced Thursday that the death toll has surpassed 30,000, with over 70,000 injured. "Tragically, an unknown number of people lie under rubble," according to the UN statement.

He reiterated calls for an immediate humanitarian ceasefire and unconditional release of all Israeli hostages in Gaza.

/CNN