U.S. officials believe the group responsible due to communications "made at the time of the incident," one official told the Post. Another official concurred, but qualified that it "was too early to draw a definitive conclusion." The ISIS affiliate was formed six years ago by "estranged members of the Pakistani branch of the Taliban," writes the Post. The "K" stands for Khorasan, "a historical region that includes parts of Afghanistan and Pakistan."
Intelligence officials had been anticipating an ISIS-K attack "for days," the Post writes, but had "limited means to thwart an assault." Late Wednesday, the government urged Americans to stay away from the Kabul airport or otherwise "leave immediately" due to "unnamed security threats," reports The Associated Press.
Although Pentagon spokesperson John Kirby has yet to confirm an official casualty count, The Wall Street Journal reported that four U.S. Marines and at least 60 Afghans were killed. Another three Marines were reportedly injured. Read more at The Washington Post.