The official called that figure a conservative estimate.

ISIS recruitment also has fallen off. It recruited only several hundred foreign fighters this year, compared with a couple thousand a month last year, CNN has learned.

In addition, the official also revealed Thursday that in May 2015, US special operations forces came “tantalizingly close” to capturing or killing ISIS leader Abu Bakr al Baghdadi in Raqqa, but failed to do so because classified information was leaked to the news media.