a few hours ago, the embassy sent out a security alert warning there are reports of the airport taking fire. i want to bring in cnn s pentagon correspondent oren liebermann. this is a very precarious situation. where are u.s. troops in-country right now? what does the pentagon say about plans if control of this airport falls, which i suppose like everything else that we ve seen, is possible? reporter: so let s be clear that if hamid karzai n international airport were to fall, that is the worst-case scenario. the need to retake an airport from insurgents or from some other group that tries to take it, that requires more troops than are on the ground now, and that s the worst-case scenario, but that s not what s happening right now. the bulk of u.s. troops are at hamid karzai international airport. there are some 3,000 troops on the ground right now. we ve just learned in the past few minutes that secretary of defense lloyd austin approved another 1,000 troops. so it will be a total o