Source: the IDF

"Just move your population of over a million impoverished people crammed into the land like sardines, just go into the borders of another US dog, it's fiiiine. Don't worry, after we flatten your homes we, the vicious colonizers, will totally give all of your land back so you can live in the rubble."

Israel isn't entitled to move an entire population of Palestinians, nor to carpet bomb Palestinian land. Besides, they will inevitably just say that lots of Hamas members went with the civilians. Also, as others said, the warning was not much of one since they were bombing immediately anyway.

Did Israel warn the civilian convoys they were going to be bombing them on the roads that they had selected as safe passage? Maybe the ambulances just ignored the warnings I'm sure.