WATCH: ‘Frantic’ Evacuations Underway at Kabul Airport With Thousands of U.S. Embassy Staff Still in Afghanistan

Troubling scenes from Afghanistan on Sunday, with the U.S. Embassy abandoned, the American flag taken down, and personnel evacuated to the Kabul airport, where they await transport out of the country.

CNN Newsroom host Jim Acosta spoke with the network’s Pentagon correspondent Oren Liebermann about the “precarious situation,” asking about what the plans were if the airport were to fall.

“So let’s be clear,” said Liebermann, “that if Hamid Karzai International Airport were to fall, that is the worst-case scenario,” and would require more U.S. troops than were on the ground right now.

There were currently about 3,000 troops on the ground in Afghanistan, he said, with the bulk of them at the airport. Secretary of Defense Lloyd Austin approved an additional 1,000 troops, which would bring total to 6,000 once they arrive.

The military’s “primary mission is clear,” said Liebermann. “It is to secure the airport such that U.S. Embassy staff and their workers can get out.”

So far, the American troops on the ground had not been fired upon, nor had they fired upon anybody, “but there is a crush of civilians, including Afghans, at the airport trying to get out of the country, and that contributes to the chaos and to the situation on the ground there.”

A senior defense official told CNN that about 500 of the U.S. Embassy staff have been able to leave Afghanistan on Sunday, with a few thousand more still to go.

Later in the show, Acosta showed video images that had been posted on social media showing Hamid Karzai airport, from which the embassy staff and other Americans were being evacuated by plane.

CNN’s Jeremy Diamond reported that President Joe Biden would address the nation “in the coming days,” although an exact date and time had not yet been announced.

“The White House knows that it needs to show that the president is on top of the situation,” said Diamond, noting that while the White House had released a statement from Biden and a photograph showing him on a video teleconference with members of his national security team, “we haven’t heard from him yet directly.”

This was “a huge milestone in U.S. history,” Diamond added, considering “the breadth and scope of this nearly two-decades-long involvement” that the U.S. had had in the war in Afghanistan, and the American people expected to hear directly from their president.

Watch the video clips above, via CNN.