Gen. Frank McKenzie, the head of U.S. Central Command, sat across from Taliban leader Abdul Ghani Baradar and showed him a map with a circle around Kabul, about 20 to 30 kilometers (12.4 to 18.6 miles) outside the city.

McKenzie told Baradar that Taliban fighters had to stay outside the circle or the United States would strike them. McKenzie explained the U.S. would finish its withdrawal as soon as possible and the Taliban must not interfere, three senior defense officials told NBC News.

The Taliban representatives agreed not to interfere, but pointed out they already had fighters inside the circle in some places, and those fighters would not leave.

McKenzie explained his mission was the safe withdrawal of Americans and allies. The Taliban leaders agreed to let Americans leave and offered to provide a liaison for security around the airport.

The next day, Taliban fighters rolled into Kabul, and no U.S. warplanes bombed the insurgents, the three senior defense officials said.