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 Palestinian death toll from the 20-month Israel-Hamas war climbed past 55,000, the Gaza Health Ministry said Wednesday, and local hospitals said at least 21 people were killed while on their way to aid distribution sites.

At least eight Palestinians who worked for the U.S-backed Gaza Humanitarian Foundation died in an ambush, the GHF said on Thursday, blaming Hamas militants for the killings that rocked the troubled food distribution operation.