The Taliban claimed responsibility for an early morning attack on the military wing of the main international airport in Kabul, which also happens to be the site of a NATO headquarters. 

As of late Sunday, the attack was still underway. There aren't any definitive reports of casualties, though the Guardian reports that at least some of the insurgents are wearing suicide vests. They were engaging in a gun battle with Afghan police forces, who responded to the attack. 

The AFP described the scene as it unfolded: 

"Loud explosions and bursts of small-arms fire erupted for at least two hours and were continuing, with the US embassy sounding its "duck and cover" alarm and its loudspeakers warning that the alarm was not a drill."

The U.S. embassy in the country issued an "emergency" warning for citizens in Afghanistan. Officials cancelled all flights to and from the airport. 

Last month, Kabul was the site of another hours-long attack with Taliban insurgents. The extremist group is apparently in the middle of what they're calling a "spring offensive" in the country, according to the BBC. They're targeting military and diplomatic sites.