A Free Syrian Army fighter runs after attacking a tank with a rocket-propelled grenade during fighting in Aleppo, Syria, in September 2012. The rebels say they are willing to take on the Islamic State, but need more weapons. Manu Brabo/AP hide caption

itoggle caption Manu Brabo/AP

Thick smoke rises following an airstrike by the U.S.-led coalition in Kobani, Syria, while fighting continued between Syrian Kurds and the militants of the self-proclaimed Islamic State, as seen from Mursitpinar on the outskirts of Suruc, at the Turkey-Syria border on Wednesday. Lefteris Pitarakis/AP hide caption

itoggle caption Lefteris Pitarakis/AP

Abdul-Rahman Kassig, who was formerly known as Peter, is shown with a truck filled with aid supplies for Syrian refugees. The American aid worker was seized by the Islamic State in October 2013 and the group is now threatening to kill him. Courtesy of Kassig Family hide caption

itoggle caption Courtesy of Kassig Family

Smoke rises after a U.S.-led coalition airstrike on Kobani, Syria, Monday, as seen from the Turkish side of the border. Kurdish fighters say they're making progress against ISIS in the area. Tolga Bozoglu/EPA/LANDOV hide caption

itoggle caption Tolga Bozoglu/EPA/LANDOV

A black flag belonging to the so-called Islamic State is seen in the Syrian town of Kobani on Thursday, as seen from the Turkey-Syria border near the southeastern town of Suruc. Umit Bektas/Reuters/Landov hide caption

itoggle caption Umit Bektas/Reuters/Landov

Alleged Islamic State militants stand next to an ISIS flag atop a hill in the Syrian town of Ain al-Arab, called Kobane by the Kurds, as seen from the Turkish-Syrian border in Suruc, Turkey, on Monday. Aris Messinis/AFP/Getty Images hide caption

itoggle caption Aris Messinis/AFP/Getty Images

Smoke rises from the Syrian town of Kobani, seen from near the Mursitpinar border crossing on the Turkish-Syrian border in the southeastern town of Suruc, Sanliurfa province, on Friday. Murad Sezer/Reuters/Landov hide caption

itoggle caption Murad Sezer/Reuters/Landov

Islamic State flags on the Mullah Abdullah bridge in southern Kirkuk earlier this week. A U.N. report says the extremist group has perpetrated possible war crimes and crimes against humanity. Reuters/Landov hide caption

itoggle caption Reuters/Landov

A Kurdish peshmerga soldier who was wounded Sept. 30 in fierce battles in nearby Nineveh province with Islamic State group militants is brought to the Zakho Emergency Hospital in Dahuk, Iraq. Hadi Mizban/The Associated Press hide caption

itoggle caption Hadi Mizban/The Associated Press

Turkish military forces of the Jandarma (police) block access at the Mursitpinar crossing gate near the Syrian border, where Syrian Kurdish people seek to pass, on Sunday. Turkey's leader says the country is willing to fight ISIS. Bulent Kilic/AFP/Getty Images hide caption

itoggle caption Bulent Kilic/AFP/Getty Images

Two Royal Air Force Tornado GR4 fighter jets prepare to take off Saturday from an airbase in Cyprus. The British warplanes were heading on their first mission over Iraq since being given parliamentary authority to strike at ISIS Friday. -/AFP/Getty Images hide caption

itoggle caption -/AFP/Getty Images

Fighters from the Islamic State group parade in their northern Syrian stronghold, Raqqa. Uncredited/AP/Raqqa Media Center hide caption

itoggle caption Uncredited/AP/Raqqa Media Center

This still image was made from video released by the U.S. military on Tuesday that shows a building hit by a U.S. airstrike in Tall Al Qitar, Syria. The U.S. is describing the bombing campaign in Syria and Iraq as a counterterrorism operation and not a war. U.S. Central Command/AP hide caption

itoggle caption U.S. Central Command/AP

Thousands of Syrians enter Turkey at Yumurtalik crossing gate near Suruc on Tuesday. The United Nations High Commissioner for Refugees has warned of a growing refugee crisis. Burhan Ozbilici/AP hide caption

itoggle caption Burhan Ozbilici/AP

Lt. Gen. William C. Mayville Jr., Joint Staff Director of Operations, speaks about airstrikes in Syria during a briefing at the Pentagon yesterday. Brendan Smialowski/AFP/Getty Images hide caption

itoggle caption Brendan Smialowski/AFP/Getty Images

Iraqi Kurdish peshmerga fighters take up positions around the town of Gwer in northern Iraq on Sept. 18. The Kurdish militia is aligned with the U.S. in the battle against the Islamic State. Mohamed Messara/EPA/Landov hide caption

itoggle caption Mohamed Messara/EPA/Landov