The number of ISIS fighters may be three times previous estimates, with between 20,000 and 31,500 fighters across Iraq and Syria,” a CIA spokesman told CNN on Thursday. Recruitment has grown stronger since June following battlefield successes and the declaration of a caliphate, he said. More than 15,000 foreign fighters, including 2,000 Westerners, have gone to Syria, coming from more than 80 countries. The US is refining its targets based on improved intelligence-gathering, including surveillance flights over Syria, a Pentagon official added. The US may also start going after ISIS leaders.