Faced with a burgeoning refugee crisis in Europe sparked by global extremism, U.S. and European officials said Tuesday there is a growing consensus that the multinational military campaign against Islamic State must focus more on targeting the group’s nerve centers in Syria.

U.S. officials initially cast the 15-month-old fight against Islamic State as an “Iraq-first” strategy, intended to stop the extremist expansion there. But Washington and its key allies are now putting a deeper emphasis on Syria.

This comes as Europe is struggling with the unabated flow of refugees and migrants fleeing conflicts in the Middle East, North Africa and South Asia where Islamic State forces are trying to extend their reach. […]