The UN chief made the comments Saturday at the opening session of an Arab summit held in Egypt's Red Sea resort of Sharm el-Sheikh.
There's an ongoing campaign of airstrikes led by Saudi Arabia in Yemen targeting the Shiite rebels, known as Houthis, and their allies.
Ki-moon also said he was angry and shamed by the failure of the world to stop Syria's raging civil war. He promised to step up diplomatic efforts.