World leaders gathering for a major summit in the shadow of a horrifying terror spree in Paris are looking to answer a critical question: Beyond tough talk, how will the world respond to bloodshed now extending far beyond the Islamic State group's foothold in the Middle East?

The specter of the Islamic State threat and Syria's civil war is hanging over the Turkish seaside city of Antalya as leaders descend for the Group of 20 summit of leading rich and developing nations.

President Barack Obama planned to discuss the IS threat with Turkish President Recep Tayyip Erdogan on Sunday. Leaders attending the summit were also to take up the issue of terrorism during a working dinner in the evening.