MANILA, Philippines (AP) — Human rights groups have asked Philippine President Rodrigo Duterte to withdraw his threat to order airstrikes against tribal schools he accused of teaching students to become communist rebels. Human Rights Watch said such an attack will constitute a war crime.

The U.S.-based group said Wednesday international humanitarian law "prohibits attacks on schools and other civilian structures unless they are being used for military purposes."

It added that "Deliberately attacking civilians, including students and teachers," is a war crime.

Left-wing Rep. Emmi de Jesus of the Gabriela Women's Party asked Duterte to retract the threat, saying government troops may use it as a pretext to attack so-called indigenous, or Lumad, schools and communities.

Duterte late Monday demanded the tribal schools in the south be abandoned and threatened to have them bombed.