ISIS-K could be able to attack U.S. in 6 months -Pentagon

Colin Kahl, under secretary of defense for policy, also said it was still "to be determined" whether the Taliban -- which is an enemy of Islamic State -- has the ability to fight Islamic State effectively following the U.S. withdrawal in August.

"The intelligence community currently assesses that both ISIS-K and al Qaeda have the intent to conduct external operations, including against the United States, but neither currently has the capability to do so. We could see ISIS-K generate that capability in somewhere between six or 12 months," he added, saying it could take al Qaeda "a year or two."