WASHINGTON (AP) — The U.N. Security Council is expected to adopt a binding resolution this week that would require nations to bar their citizens from traveling abroad to join terrorism organizations, part of a U.S.-led effort to galvanize the international community against what Obama administration officials call an “unprecedented” threat from extremists flocking to Syria and Iraq.

Obama administration officials touted the measure, which they said had been negotiated over several months, as a significant step in their strategy against the Islamic State group and other militant organizations that are drawing Europeans, Americans into their violent orbit. But they acknowledged that the UN resolution has no enforcement mechanism and that the international community has no single definition of what constitutes a terrorist group.