American journalist Steven Sotloff (left) talks with Libyan rebels on the Al Dafniya front line on June 2, 2011, in Misrata, Libya. Sotloff was kidnapped in August 2013 near Aleppo, Syria. Etienne de Malglaive via Getty Images hide caption

itoggle caption Etienne de Malglaive via Getty Images

Secretary of Defense Chuck Hagel (left) and Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey during a Pentagon briefing on Thursday. Hagel said Islamic State militants in Iraq and Syria posed a threat "beyond anything we've seen." Yuri Gripas/Reuters/Landov hide caption

itoggle caption Yuri Gripas/Reuters/Landov

This image posted on a militant website shows ISIS fighters marching in Raqqa, Syria, where the extremist group trains recruits, including Westerners. AP hide caption

itoggle caption AP

President Obama leaves after making a statement Wednesday about the killing of journalist James Foley in Syria. The president said the U.S. would continue to confront Islamic State extremists despite the brutal murder. Jacquelyn Martin/AP hide caption

itoggle caption Jacquelyn Martin/AP

President Obama said Wednesday that the extremist group that carried out the beheading of U.S. journalist James Foley engages in "cowardly acts of violence" and "has no place in the 21st century." Kevin Lamarque/Reuters/Landov hide caption

itoggle caption Kevin Lamarque/Reuters/Landov