Turkey's president on Wednesday vowed to expand its operation against U.S.-allied Kurdish forces in northern Syria toward the town of Manbij, which would bring Turkish troops and their Syrian allies closer to U.S. forces supporting the Kurds against the Islamic State group.

Turkey launched an incursion Saturday against the Afrin enclave, which is controlled by a Kurdish militia that played a key role in U.S. efforts to roll back the extremist group. U.S. forces are based in Kurdish-held parts of northeastern Syria but not in or near Afrin.