Witnesses and medics in Gaza say Israeli forces have killed at least 22 people and wounded 20 others when they fired on crowds returning from a food aid site and at a United Nations warehouse.

The Israeli military acknowledged on Monday that Palestinian civilians were harmed at aid distribution centres in the Gaza Strip, saying that new instructions had been issued to Israeli forces following "lessons learned".

Dozens of Palestinians have died in several rounds of Israeli airstrikes from Friday night until Saturday morning, officials said.