France on Saturday said it condemned "in the firmest of terms" an Israeli strike on a religious school housing displaced people in Gaza that rescuers said killed 93 people.

"For several weeks, school buildings have been repeatedly targeted, with an intolerable number of civilian victims," the French foreign ministry said.

"Israel must respect international humanitarian law," it added.

AFP could not independently verify the toll.

But if confirmed, it would appear to be one of the largest from a single strike during 10 months of war between Israel and Hamas Palestinian militants.