France, Russia and the U.S. moved beyond talk of cooperation and into the far more difficult realm of action, as the “grand and single coalition” French President François Hollande called for to combat Islamic State began coming into view.

President Barack Obama said Wednesday that if Russia shifts its military strategy in Syria to focus on Islamic State, the U.S. would welcome cooperation with Moscow on an intensified military campaign. He said he conveyed that message to Russian President Vladimir Putin in a meeting in Turkey...