The Organisation of Islamic Cooperation, after a meeting of its executive committee in the Saudi city of Jeddah, said it was forming a ministerial team to lobby the Security Council and international community "to halt the Israeli aggression".
The 57-member OIC said it would also push for an urgent meeting of the UN Human Rights Council in Geneva to investigate "the crimes of occupying power Israel and its violations of the rights of Palestinians".
In New York, meanwhile, UN chief Ban Ki-moon appealed for a ceasefire between Israel and Palestinian militants.
"It is now more urgent than ever to try to find common ground for a return to calm and a ceasefire understanding," he told an emergency meeting of the Security Council.
Ban said all parties, including Palestinian armed groups, must respect international law.
In the worst confrontation since 2012, Israel has launched hundreds of air strikes on Gaza over three days, killing more than 80 Palestinians, in the face of cross-border rocket fire by militant groups.
