Mr Ban said that those responsible should be held accountable and demanded a "full investigation" through proper judiciary systems.
He was speaking in front of the smouldering remains of the UN food warehouse destroyed by Israeli shells.
He said he would do all he could to help the population of Gaza.
Mr Ban is the first international leader to visit Gaza for several years, entering through the Israeli-controlled Erez crossing and driving through the bomb-damaged northern suburbs to Gaza City. More...