A spokesman for the military wing of the main resistance group Hamas made the statement on Monday hours after one Palestinian girl was killed with a bullet to the head and another was wounded while lining up for classes in a schoolyard in Gaza.
"Eight resistance groups will resume their attacks against Israel if the Israeli agression does not immediately stop," an Izz al-Din al-Qassam spokesman said in a phone call to AFP.
The caller, who said he was speaking on behalf of eight factions, said a statement would be issued shortly.
Earlier on Monday, witnesses said 10-year-old Nuran Did was lining up with classmates to enter their school in the morning when she was shot from the Israeli occupation army's Termit post, 900m away.
"She suddenly screamed and fell to the ground, bleeding. The girls started to run everywhere," one witness said.
The Palestinian resistance group Hamas said it fired five mortar shells at a Jewish settlement in the Gaza Strip in retaliation for the girl's death.
An Israeli military spokeswoman had no immediate information on the incident near the border with Egypt, where Israeli soldiers and resistance fighters have frequently clashed during a four-year-old Palestinian uprising.