U.S. officials strongly believe the ISIS-Khorasan group was behind the attack on Thursday at Kabul's airport, a source familiar with congressional briefings on Afghanistan said on Thursday.
A second U.S. government source familiar with intelligence activities said that while the U.S. government is still investigating, the airport attack has "all the hallmarks" of an ISIS-K attack.
(Reporting by Mark Hosenball, writing by Patricia Zengerle; editing by Chizu Nomiyama)
