GAZA - At least 12 Palestinians were killed on Sunday by Israeli airstrikes and gunfire across the Gaza Strip, including civilians near humanitarian aid distribution sites, according to local health officials.

A CNN investigation into a deadly incident near an aid distribution site in southern Gaza on Sunday points to the Israeli military opening fire on crowds of Palestinians as they tried to make their way to the fenced enclosure to get food.

At least 27 Palestinians were killed near a Gaza food distribution hub operated by a controversial U.S.-backed group, the enclave's Hamas-run health ministry says.

The aid system rolled out last month has been marred by chaos and violence, while the UN system has struggled to deliver food because of Israeli restrictions and a breakdown of law and order, despite Israel loosening a total blockade it imposed from early March to mid-May.

Palestinian health officials and witnesses say Israeli forces fired on people as they headed toward an aid distribution site on Tuesday, killing at least 27, in the third such shooting in three days.