A new assessment from the CIA on Thursday said that the Islamic State of Iraq and the Levant (ISIL or ISIS) "can muster between 20,000 and 31,500 fighters across Iraq and Syria," a CIA spokesman told USA Today.
The estimate is up to triple the previous estimate of 10,000.
"CIA assesses the Islamic State of Iraq and the Levant can muster between 20,000 and 31,500 fighters across Iraq and Syria, based on a new review of all-source intelligence reports from May to August, an increase from our previous assessment of at least 10,000 fighters," said CIA spokesman Ryan Trapani.
"This new total reflects an increase in members because of stronger recruitment since June following battlefield successes and the declaration of a caliphate, greater battlefield activity, and additional intelligence."
The details about the increased number of fighters come as the Pentagon refines its intelligence on the area, including surveillance flights underway over Syria.
CNN reported that the number of fighters is also on the rise because it includes those freed from prisons by ISIL. More than 15,000 fighters from 80 countries have gone to Syria, a CIA source said. He said it was unclear whether the foreigners went to Syria to be part of ISIL or to fight against it.