Yuri Gripas/REUTERS
Secretary of Defense Chuck Hagel said that the United States is aware of Americans who are serving with ISIS in Iraq and Syria. “Over 100 U.S. citizens who have U.S. passports who are fighting in the Middle East with ISIL forces," Hagel said Wednesday on CNN. "There may be more, we don't know." Following ISIS’s execution of American journalist Steven Sotloff, Hagel stressed the need for an aggressive response to the self-proclaimed Islamic State. "They control half of Iraq today. They control half of Syria today,” he said. “We better be taking them seriously." Earlier on Wednesday, President Obama spoke withe reporters about the U.S.'s commitment to fighting ISIS. “Those who make the mistake of harming Americans will learn that we will not forget and that our reach is long and that justice will be served,” he said. Vice President Joe Biden said the U.S. will follow ISIS to the “gates of hell until they are brought to justice because hell is where they will reside.”