Witnesses reported on Sunday that Israeli forces fired on Palestinians waiting to receive aid close to a distribution site in Gaza.
At least 21 were killed and scores more injured, according to a Red Cross field hospital and numerous witnesses, cited by The Associated Press.
Hamas said that in total 30 people had been killed and a dozen more injured.
"There was fire from all directions, from naval warships, from tanks and drones," The Associated Press cited Amr Abu Teiba, who was in the crowd, as saying. Another eyewitness corroborated the account.
The incident happened on Sunday morning as people gathered to receive food. The population of the Palestinian enclave has been starved by a monthslong Israeli blockade that sparked international outrage, even from some of Israel's closest allies.
The decision by the Israeli government to allow aid into Gaza has also been mired in controversy and chaos. The UN said that the first deliveries of aid had been minimal and even then failed to reach the people in need.
An Israeli and US-backed plan to send in the Gaza Humanitarian Foundation (GHF) has not assuaged concerns. The aim was to avoid aid being diverted to Hamas — something the UN has said there is no evidence for — and as such, the GHF employs private security contractors, similar to mercenaries, to protect the aid distribution sites.
The Foundation on Sunday said it had distributed aid "without incident," and dismissed what it referred to as "false reporting about deaths, mass injuries and chaos."
Local health officials have reported that prior to Sunday, six people had been killed and several more wounded by live fire at GHF distribution sites.
UN agencies have refused to work with the GHF, saying it violates humanitarian rules by giving Israel control over who receives aid.
