Central Intelligence Agency director John Brennan said Thursday that, years into the United States' fight against the Islamic State, the terrorist group's reach and power have not been diminished and that it has even more fighters than al-Qaeda had at its height.

Speaking to the Senate Intelligence Committee, Brennan said, "Unfortunately, despite all our progress against ISIL on the battlefield and in the financial realm, our efforts have not reduced the group's terrorism capability and global reach. The resources needed for terrorism are very modest, and the group would have to suffer even heavier losses of territory, manpower, and money for its terrorist capacity to decline significantly."

He also said the group is still "a formidable adversary," adding, "The branch in Libya is probably the most developed and the most dangerous."

He also projected that it "will intensify its global terror campaign to maintain its dominance of the global terrorism agenda."

And, despite the apparent failure of the military strategy, Brennan said "a long and difficult fight" would continue against the group whose number of fighters now "far exceeds what al-Qaeda had at its height."

His comments confirm warnings from many on the left that a military strategy to defeat ISIL, or ISIS, as it is also known, would only foment further acts of terrorism. Institute for Policy Studies fellow Phyllis Bennis, for example, warned in 2014, when President Barack Obama said he authorized new U.S. military airstrikes in Iraq to target ISIS, "it should be eminently clear that we cannot bomb Islamist extremists into submission or disappearance. Every bomb recruits more supporters."

And Jeremy Scahill, co-founding editor of the The Intercept and author of the book Dirty Wars: The World is a Battlefield, previously called Obama's war on ISIS an "epic formula for blowback."