Updated

The Pentagon warned Tuesday of a swift response to any attack carried out by the Taliban against the mission to evacuate U.S. personnel and Afghan allies from Afghanistan as flights out of Kabul's airport resumed Tuesday. 

The current U.S. mission in Afghanistan was announced by President Biden on Monday, who said it would be "short in time, limited in scope and focused on our objectives: get our people and our allies as quickly and as safely as possible." 

A White House official told Fox News Tuesday that military and civilian flights from Hamid Karzai International Airport in Kabul are resuming. 

The official said that over the last 24 hours, the U.S. has been able to move more than 700 people out of Afghanistan, including 150 American citizens. 

The official said the State Department has sent messages to some American citizens in Afghanistan sharing information with them on how to safely assemble at the airport for flights out. 

EVACUATION FLIGHTS ONGOING OUT OF KABUL

Pentagon spokesman John Kirby on Tuesday during an interview with CNN said the U.S. has been able to bring in about 1,000 more U.S. troops, bringing the total footprint to roughly 3,500. 

U.S soldiers stand guard along a perimeter at the international airport in Kabul, Afghanistan, Monday, Aug. 16, 2021. (AP Photo/Shekib Rahmani)

U.S soldiers stand guard along a perimeter at the international airport in Kabul, Afghanistan, Monday, Aug. 16, 2021. (AP Photo/Shekib Rahmani) (AP Photo/Shekib Rahmani)

"Things are back up and running," Kirby said. "We're going to keep flowing forces to make sure that we can ensure a safe and secure environment for operations at the airport." 

A White House official told Fox News that more U.S. troops will arrive in Afghanistan Tuesday and Wednesday. 

Flights were temporarily suspended from Kabul International Airport on Monday as U.S. forces attempted to gain control of the crowd of Afghans desperate to leave the country. U.S. officials told Fox News Monday that the runway was "not secure" as hundreds of Afghans "breached" the airport walls and flooded the runway. 

The Pentagon, at this point, believes it can move between 5,000 and 9,000 people out of Kabul on military aircraft per day. Kirby said the Pentagon wants the civilian side of the airport to remain open so that commercial and charter flights can fly in and out as well. 

Kirby said the U.S. has "three bases for up to 22,000 people in the next couple of weeks." 

"If we have to go more, higher than that, we will certainly do that," Kirby said, referring to not only special immigrant visa applicants from Afghanistan but also their families. "We're committed to their families as well." 

As for any potential disruption to the U.S. mission by the Taliban, the Pentagon echoed the same dire warning Biden made Monday. 

"If we are attacked by the Taliban or about anybody else in our mission in Afghanistan, we're going to respond accordingly and appropriately, swiftly and, as the president said, forcefully," Kirby said. "We have capabilities there at the airport to do that. We are flowing in additional capabilities to provide for the defense of the airport and for the operations there." 

"I'm not going to speculate or hypothesize about wherever individual operations might be, but we certainly had the capabilities on hand and we're gaining more of those capabilities, more combat power, over the coming couple of days," Kirby continued. 

BIDEN STANDS ‘SQUARELY BEHIND’ DECISION TO WITHDRAW US TROOPS FROM AFGHANISTAN

"Any attack on our people, or on our operations at the airport, will be met with a swift and forceful, an unambiguous response," Kirby added. "And I think I'm just gonna leave it at that." 

Former senior defense officials in contact with commanders on the ground in Kabul have told Fox News that the Taliban has "a ring outside of the airport and won't let anyone inside it." 

"The big issue here is that no people outside of the Taliban ring will get in," an official told Fox News. 

Separately, an Afghan who is also a former State Department contractor told Fox News that Taliban fighters have established checkpoints throughout the city and around the airport.  Some, he said, have been beating people on the way to the airport.

When the former contractor encountered a checkpoint, the Taliban guard let him go but warned him not to leave the country: "You can go, don’t run away," he said.

He described the chaotic scene at the airport Monday: "There was kids, women, babies, old women, they could barely walk," the Afghan said. "They were very very bad situation, I'm telling you. At the end, I was thinking that there was like 10,000 or more than 10,000 people and they’re running into the airport … The Taliban (were) beating people and the people were jumping from the fence, the concertina wire, and also the wall."

He said Taliban fighters are going through neighborhoods looking for those who worked with the U.S. government, and that some were asking his neighbors about him.

Meanwhile, the president, addressing the nation Monday, said he stands "squarely behind" his decision to withdraw U.S. troops from Afghanistan after having a presence for 20 years, while admitting that the fall of the country to the Taliban "did unfold more quickly than we had anticipated." 

Biden placed blame on the Afghan leadership for the country's plight, saying that Afghan President Ashraf Ghani had refused advice to negotiate and erroneously insisted Afghan forces would fight. 

"American troops cannot, and should not, be fighting in a war and dying in a war that Afghan forces are not willing to fight for themselves," Biden said Monday, adding that the U.S. has given "every tool they could need."

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"We gave them the chance to determine their own future," he said. "What we could not provide them was the will to fight for that future." 

Biden has authorized 6,000 U.S. troops to deploy to Afghanistan to assist in the evacuation of U.S. personnel and Afghan allies, as the Taliban pushes to restore the Islamic Emirate of Afghanistan – the formal name of the country under the Taliban rule before the militants were ousted by U.S.-led forces in the wake of the 9/11 attacks. The attacks on Sept. 11, 2001, were orchestrated by al Qaeda while it was being sheltered by the Taliban in Afghanistan. 

Fox News' Bret Baier and Rich Edson contributed to this report.