The UN human rights office said on Tuesday that the "weaponization" of food for civilians in Gaza constitutes a war crime, in its strongest remarks yet on a new model of aid distribution run by an Israeli-backed organization.

Over 410 people have been killed by gunshots or shells fired by the Israeli military while trying to reach distribution sites of the Gaza Humanitarian Foundation since it began work in late May, UN human rights spokesperson Thameen Al-Kheetan told reporters at a Geneva press briefing.

The death toll has been independently verified by his office, he added.

"Desperate, hungry people in Gaza continue to face the inhumane choice of either starving to death or risk being killed while trying to get food," he said, describing the system as "Israel's militarized humanitarian assistance mechanism".

"The weaponization of food for civilians, in addition to restricting or preventing their access to life-sustaining services, constitutes a war crime and, under certain circumstances, may constitute elements of other crimes under international law."

Asked whether Israel was guilty of that war crime, he said: "The legal qualification needs to be made by a court of law."

Israel rejects war crimes charges in Gaza and blames Hamas fighters for harm to civilians for operating among them, which the fighters deny.