The volume of aid delivered to Gaza has collapsed in recent weeks as Israeli airstrikes have targeted police officers who guard the convoys, U.N. officials say, exposing them to looting by criminal gangs and desperate civilians.

After a string of Israeli attacks on members of Gaza’s Hamas-run civilian police force, officers withdrew earlier this month from the Palestinian side of the Kerem Shalom crossing with Israel. Since they left, trucks have been attacked in the crossing’s holding area, according to U.N. humanitarian coordinator James McGoldrick. Drivers have been shot at, attacked with axes and box cutters, and had their windows smashed, he said.

Humanitarian officials said police have also stopped serving as security guards for aid convoys, paralyzing deliveries in the enclave, where some hungry families have resorted to eating weeds and animal feed and profiteers are selling stolen food at astronomical rates on the black market.

“With the departure of police escorts it has been virtually impossible for the U.N. or anyone else … to safely move assistance in Gaza because of criminal gangs,” U.S. Ambassador David Satterfield, appointed by President Biden to coordinate humanitarian aid to Gaza, said Friday.

Satterfield said Israeli forces had killed as many as nine Palestinian police officers involved in protecting aid convoys, including a commander. Police include “Hamas elements” he said, but also people who are politically unaffiliated and remnants of Palestinian Authority forces.

Three police officers were killed by an Israeli airstrike in Rafah on Feb. 10, according to Rafah governorate police and eyewitnesses, as they were driving to monitor the distribution of food aid in Tal al-Sultan, west of Rafah.