A member of the Syrian Democratic Forces, the rebel group backed by the U.S.-led coalition, looks out upon the ruins of Raqqa last October, toward the end of the coalition's campaign to dislodge the Islamic State from its former stronghold. Bulent Kilic/AFP/Getty Images hide caption
Young men outside Raqqa, Syria, training to find and destroy hidden explosive devices left by retreating ISIS forces. Greg Dixon/NPR hide caption
American-backed forces took control of the Islamic State's de facto capital of Raqqa, Syria, last month, dealing a major blow to the extremist organization. Bulent Kilic/AFP/Getty Images hide caption
A picture taken on Oct. 20, 2017, shows writing about the so-called Islamic State group on a wall in the recaptured Syrian town of Mayadeen. The Red Cross is urging lawful treatment of foreign fighters who traveled to Syria to join the extremists. AFP/Getty Images hide caption
A member of the Syrian Democratic Forces walks on a building near Raqqa's stadium Monday, as they cleared the last positions on the front line in the fight against ISIS. Bulent Kilic/AFP/Getty Images hide caption
Syrian Democratic Forces fighters opening fire on an Islamic State group's position in March in the countryside east of Raqqa, Syria. AP hide caption
Members of the Syrian Democratic Forces look toward Tabqa, Syria. The U.S. announced Tuesday that it will begin arming Kurds allied with the SDF as the Pentagon prepares an offensive to retake the ISIS stronghold Raqqa. Syrian Democratic Forces via AP hide caption
Central Command says an errant coalition strike killed 18 fighters from the Syria Democratic Forces. A member of the U.S.-backed SDF, made up of an alliance of Arab and Kurdish fighters, inspect the Tabqa dam on March 27. Delil Souleiman/AFP/Getty Images hide caption
This photo, released by the Syrian official news agency SANA, shows bloodied streets and damaged buses after a bombing in Damascus on Saturday. SANA via AP hide caption
U.S.-backed fighters rest during fighting with the Islamic State group near Ein Issa, north of Raqqa, Syria, as shown in a video by Qasioun, a Syrian opposition media outlet. AP hide caption