Human rights organization B'Tselem issued a statement Monday calling on Hamas leaders in the Gaza Strip to investigate claims its members committed war crimes against Fatah supporters, and put the suspects on trial.

The organization said that both parties committed severe violations of customary international humanitarian law during fighting in the Gaza Strip over the past week, including acts that constitute war crimes.

B'Tselem charged both factions with summary execution of opponents' supporters, and of civilians not involved in the fighting.

The organization said reports were made of serious abuse preceding the executions. Both parties had also deliberately attacked hospitals.

The group warned against retaliatory attacks and arbitrary arrests of Hamas members and institutions in the West Bank, now controlled by an emergency cabinet formed by Palestinian Authority Chairman Mahmoud Abbas.

It said the Palestinian Authority must use all means at their disposal to prevent such attacks.

B'Tselem also reminded the Israeli government that it "bears overarching responsibility for the human rights of all people in the West Bank, including for acts committed by agencies operating with Israel's agreement, including the Palestinian Authority."