CIA estimates IS has up to 31,500 members

The Islamic State (IS) terrorist group has between 20,000 and 31,500 fighters in Iraq and Syria, much higher than the previous estimate, the U.S. spy agency Central Intelligence Agency (CIA) said Thursday.

The Islamic State (IS) terrorist group has between 20,000 and 31,500 fighters in Iraq and Syria. [Video clip]

The latest estimate was based on "a new review of all-source intelligence reports from May to August," CIA spokesman Ryan Trapani said in a statement.

The new figure is much higher than the previous estimate of about 10,000 IS fighters.

"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 statement said.

The CIA statement was issued one day after U.S. President Barack Obama announced in a speech Wednesday night a comprehensive plan to expand airstrikes against IS forces and rely on an international coalition to degrade and ultimately destroy the terrorist group.

The IS, also known as the Islamic State of Iraq and Syria (ISIS), has drawn alarm after overrunning vast swaths of territory in Iraq in a bid to set up their own nation-state ruled by radical Islamic laws.

It even beheaded two U.S. journalists and posted videos of their horrific executions online.

The terrorists have also threatened to "raise the flag of Allah in the White House," to the alarm of Americans 13 years after the Sept. 11, 2001 attacks on New York and Washington that claimed nearly 3,000 lives.

Meanwhile, American forces continued to attack the IS targets in Iraq, launching two airstrikes on Wednesday and Thursday near the Mosul Dam in support of Iraqi Security Forces, the U.S. Central Command said Thursday. The strikes destroyed two IS machine gun emplacements and an IS bunker.

Since Aug. 7, U.S. forces have conducted a total of 156 airstrikes against IS targets across Iraq.