Pentagon spokesperson John Kirby also verified the news in a tweet.
"This is truly a nighmare scenario," said ABC News' Chief Global Affairs Correspondent Martha Raddatz. "You have a deadline of American forces getting out of there ... and now this explosion at one of those gates. It will surely shut down that whole area, and here will be a lot of questions about what the U.S. does next."
U.S. officials had for days been warning of the "very real possibility" of an attack from terrorist group and sworn Taliban enemy ISIS-K — earlier, the Embassy had warned Americans to stay away from the airport, and cautioned anyone outside the perimeter to "leave immediately" due to "unnamed security threats," per The New York Times. The British and Australian governments issued similar warnings.
The State Department "worried about this exact scenario," said Raddatz, which is why security alerts were "so urgent and so imminent." There has been no official casualty count, but a witness told The Associated Press that "several people appeared to have been killed or wounded." Read more at The Associated Press.