Just 18, Hamad al-Tamimi says he was a religious studies student in Riyadh, Saudi Arabia, before jihadists influenced and recruited him online. Now he's in the hands of Iraqi authorities, accused of being an ISIS fighter captured in Iraq's west. Al-Tamimi is one of numerous foreign fighters believed to have swelled the Sunni extremist group's ranks in recent months. On Thursday, the CIA made a startling announcement: The number of people fighting for ISIS may be more than three times the previous estimates. And among their ranks are foreign fighters -- those such as al-Tamimi. A dramatic rise Analysts and U.S. officials initially estimated there were as many as 10,000 fighters, including those freed from prisons by ISIS and Sunni loyalists who joined the fight as the group advanced across Iraq.
@highlight
Pentagon spokesman: Higher ISIS estimate doesn't change military approach
@highlight
ISIS can "muster between 20,000 and 31,500 fighters" across Iraq, Syria, the CIA says
@highlight
The White House says retired Gen. John Allen will lead international effort against ISIS
@highlight
Iraqi Prime Minister: French President says France will strike ISIS targets in Iraq
A @placeholder source told CNN this week that more than 15,000 foreign fighters, including 2,000 Westerners, have gone to Syria.