From the US embassy in Afghanistan. US Citizens requesting assistance have to register by completing a Repatriation Assistance Request?
Location: Kabul
Security Alert – U. S. Embassy Kabul, Afghanistan
Event: The security situation in Kabul is changing quickly including at the airport. There are reports of the airport taking fire; therefore we are instructing U.S. citizens to shelter in place.
U.S. citizens wanting assistance in departing the country should register for any option that might be identified to return to the United States, and must complete this Repatriation Assistance Request for each traveler in their group. Spouses and minor children of U.S. citizens in Afghanistan who are awaiting immigrant visas should also complete this form if they wish to depart. Please do so as soon as possible. You must complete this form even if you’ve previously submitted your information to the U.S. Embassy in Kabul. Do not call the U.S. Embassy in Kabul for details or updates about the flight. This form is the only way to communicate interest in flight options.
https://af.usembassy.gov/security-alert-u-s-embassy-kabul-afghanistan-15/