WASHINGTON — With top-level meetings underway at the United Nations to determine a plan for confronting the Islamic State, blocks away, a star-studded panel launched a nongovernmental initiative to confront what it described as a “growing threat from extremist ideology.”

During a press conference Monday morning, former world leaders and top diplomats gathered to launch the Counter Extremism Project, a private-sector organization that describes itself as nonpartisan in its efforts to combat extremism.