An Israeli airstrike on aid workers delivering food in Gaza has killed at least seven people — including citizens of Australia, Poland, the United Kingdom and a U.S.-Canada dual citizen — in the latest Israeli military action to hit humanitarian efforts in the besieged Palestinian territory.

World Central Kitchen, the food charity founded by celebrity chef José Andrés, said early Tuesday it was immediately suspending operations in the region, delivering a blow to the recently opened sea route for food aid. Ships carrying food turned back from Gaza after arriving just a day earlier.

Israel says the strike was an accident and that officials are investigating.

The United States, which has provided key military and diplomatic support for Israel’s war against Hamas in Gaza, had hoped the sea route would allow more food to enter the territory. In northern Gaza, the United Nations says much of the population is on the brink of starvation.

Related Story: Israeli Military Withdraws From Gaza’s Largest Hospital After Leveling It

The airstrike late Monday came hours after Israeli forces withdrew from the burnt-out ruins of Shifa Hospital in northern Gaza, allowing Palestinians and journalists to survey the devastation after a two-week raid that destroyed what was once the largest medical center in the Gaza Strip. The Israeli military says the raid targeted Hamas militants grouped inside, a claim that could not be independently confirmed.

Death Toll in Gaza

Israel’s war in Gaza has killed nearly 33,000 Palestinians, the territory’s Health Ministry says. The ministry doesn’t differentiate between civilians and combatants in its tally, but says women and children make up two-thirds of the dead. The war began on Oct. 7, when Hamas-led militants stormed into southern Israel, killing some 1,200 people, mostly civilians, and taking around 250 people hostage.