A person looks at a vehicle where employees from the WCK were killed in an Israeli airstrike in Gaza on Tuesday. Reuters

Israel’s defence chief said Wednesday a strike that killed seven aid workers in Gaza was a "grave mistake", after the deaths prompted a chorus of international outrage.

"This incident was a grave mistake," IDF chief Herzi Halevi said in a video message after the strike that hit a World Central Kitchen (WCK) convoy delivering aid on Monday.

"It shouldn't have happened," Halevi said, as he blamed the strike on a nightime "misidentification".

"We are sorry for the unintentional harm to the members of WCK."

AFPTV footage from the scene showed the punctured roof of a vehicle emblazoned with WCK's logo alongside the mangled wreck of other vehicles.

Since the October start of the war, the US-based charity had been involved in feeding displaced Gazans, and was one of two organisations spearheading the delivery of food aid arriving by sea.

The employees killed on Monday had just unloaded "more than 100 tons of humanitarian food aid brought to Gaza on the maritime route," WCK said.

The attack, which killed Australian, British, Palestinian, Polish and US-Canadian staff, was widely condemned, with world leaders demanding an investigation.

In a strongly worded statement, US President Joe Biden said Israel "has not done enough to protect aid workers trying to deliver desperately needed help to civilians."

He called for a "swift" investigation to bring accountability to what he said was not a "stand alone incident".

UN Secretary-General Antonio Guterres told the General Assembly that 196 humanitarian workers have been killed in the war.

He called the strike "unconscionable" but "an inevitable result of the way the war is being conducted".

"It demonstrates yet again the urgent need for an immediate humanitarian ceasefire."

Agence France-Presse