"Let me be clear, any American who wants to come home, we will get you home," Biden said.
"Make no mistake, this evacuation mission is dangerous and involves risks to our armed forces. And it's being conducted under difficult circumstances. I cannot promise what the final outcome will be, or what it will be that it will be without risk of loss.," Biden continued. "But as commander in chief, I can assure you that I will mobilize every resource necessary."
Biden also said that the United States is open to using the military to help Americans unable to get to the airport while simultaneously warning of potential pitfalls in Americans' operation and saying he "cannot promise what the final outcome will be."
Among the unknowns is where there could be terrorist attacks outside the Kabul airport, Biden said. He also noted that his administration is not sure of the number of Americans actually in Afghanistan.
The government is working "to verify the number of Americans still in country as we work on this," the president said.
"Because we're not, don't know the exact number of people who may have been there, and those who may have come home to the United States." Biden added. "We want to get a strong number as to exactly how many people are there, how many American citizens, and where they are."
The Pentagon revealed this news Thursday. Department of Defense Spokesman John Kirby said, "I don't know," how many Americans there are left for the military to evacuate. He said that the State Department would have a more accurate number. But even it wouldn't know for sure, Kirby said, because Americans in Afghanistan have no "obligation that they register their presence."
Biden also Friday defended his decision to withdraw from American troops from Afghanistan, arguing that the outcome could not have been better if American troops left the country several years ago or several years in the future. And he said that he is not worried about critics of how he's handling the withdrawal from Afghanistan, but instead finishing the mission of getting Americans out of the country that's now controlled by the Taliban.
"There'll be plenty of time to criticize and second guess when this operation is over, but now I'm focused on getting this job done," he said.
Biden notably took questions from White House reporters for the first time since Afghanistan fell to the Taliban, after two conferences earlier this week in which he didn't. The president was asked about several elements of the withdrawal, including whether Americans lost credibility around the world due to how it was handled.
"I have seen no question of our credibility from our allies around the world," Biden said. "I've spoken with our NATO allies… The fact of the matter is I have not seen that – matter of fact the exact opposite I've gotten. Exact opposite thing is we're acting with dispatch, we're acting, committing to what we said we would do."
And asked whether the U.S. might use the military to run rescue missions outside of the Kabul airport, Biden said he is open to the possibility.
"We're considering every every opportunity and every means by which we could get folks to the airport," he said.
Fox News' Adam Shaw contributed to this report.