At least 51 Palestinians were killed and over 200 wounded in the Gaza Strip while waiting for U.N. and commercial trucks to enter the territory with desperately needed food, according to Gaza’s Health Ministry and a local hospital.

Multiple aid workers were killed after a bus was attacked in Gaza on Wednesday night, according to a US-backed humanitarian aid organization which accused Hamas of carrying out the assault.

The group, which has been harshly criticized by the U.N. and other aid providers, said at least five people had died in an attack on one of its buses.