Biden says military withdrawal from Afghanistan will conclude Aug. 31

President Joe Biden announced Thursday the drawdown of the U.S. military presence in Afghanistan will be completed by Aug. 31, as instability and violence ratchet up in the region.

"Our military mission in Afghanistan will conclude on Aug. 31. The drawdown is proceeding in a secure and orderly way, prioritizing the safety of our troops as they depart," he said.

"We did not go to Afghanistan to nation-build. And it's the right and the responsibility of Afghan people, alone, to decide their future and how they want to run their country," the president continued.

Biden said it was time to end the nation's longest war, noting "2,448 Americans killed, 20,722 more wounded and untold thousands coming home with unseen trauma to their mental health," adding, "I will not send another generation of Americans to war in Afghanistan with no reasonable expectation of achieving a different outcome."

Asked if a Taliban takeover of Afghanistan is now inevitable, Biden said it isn't because "the Afghan troops have 300,000 well-equipped, as well-equipped as any army in the world, and an air force, against something like 75,000 Taliban."

"It is not inevitable," he repeated.

Prior to delivering the speech, Biden and Vice President Kamala Harris received a briefing on the drawdown from their national security team.

The White House has stood firm in defense of Biden's decision to pull out, citing internal analysis concluding that a military solution to the conflict in Afghanistan is unlikely.

But the Taliban are continuing to gain ground, with an aggressive summer offensive through northern provinces in recent weeks that has seized control of dozens of districts.

Biden administration officials have also defended the military withdrawal by saying that U.S. intelligence indicated the threat to U.S. forces from Taliban militants would have significantly increased throughout summer.

"When he announced our drawdown, he made clear that the Taliban would have been shooting at U.S. troops again after May 1. And the withdrawal deadline negotiated by the previous administration kind of set that timeline," Psaki said July 2, adding that an administration review of options to advance U.S. interests in Afghanistan "did not sugarcoat what the likely outcomes would be" with continued engagement in the region.

The withdrawal, which Biden had said would wrap up by Sept. 11, unfolded ahead of schedule. Bagram Air Base, the main hub of military operations in Afghanistan for the past two decades, was handed over to Afghan forces July 2. In a statement on Monday, U.S. Central Command indicated the withdrawal was about 90% complete. A small force of about 650 will remain in Afghanistan after the withdrawal to protect the U.S. Embassy and, for now, the Kabul airport.

"Our presence is small, both materially and physically," Pentagon press secretary John Kirby said Tuesday.

But since U.S. troops began pulling out of Afghanistan, security has rapidly deteriorated. Taliban militants have swept through dozens of districts, seizing control and either slaughtering Afghan troops or winning their surrender. Hundreds of Afghan forces also fled across the northern Afghan border into Tajikstan when faced with the growing Taliban threat, although they are now expected to return to the country. Some have already been flown back into Afghanistan.

Amid the recent clashes, the Biden administration is still emphasizing a negotiated settlement between the Taliban and the Afghan government. Those talks, hosted in Doha, Qatar, have been all but dead since they began last September and reached an agenda in November.

The two sides met again Wednesday in Tehran and agreed that "war is not the solution to Afghanistan’s problems," according to the Taliban spokesperson in Doha.

In those districts retaken by the Taliban last month, militants have evicted families and looted and torched their homes, according to Human Rights Watch, allegedly in retaliation for working with the Afghan government.

There is also concern for the safety of thousands of translators, drivers and other Afghans who assisted U.S. forces and diplomats during the war and are now targets of Taliban militants. In his remarks Thursday, Biden spoke directly to that population to assure them of U.S. support.

"Starting this month...we're going to begin relocation flights for Afghanistan SIV applicants and their families who choose to leave. We have a point-person in the White House and at the State Department-led task force coordinating all these efforts," Biden said.

"Our message to those women and men is clear: There is a home for you in the United States, if you so choose, and we will stand with you just as you stood with us," he added.

While the Biden administration has confirmed it is working to move some of the affected Afghans out of the country to safe locations to await special immigrant visas that would allow them to move to the U.S., the administration has not specified how many will be moved, how quickly or where.

A U.S. official confirmed to ABC News on Friday that the group may be moved to Tajikistan, Uzbekistan and Kazakhstan -- three of Afghanistan's northern neighbors in Central Asia -- but stressed the planning was still early and no decisions had been made. A second U.S. official confirmed Thursday the list also includes Qatar and the United Arab Emirates.

Biden hosted his Afghan counterpart, President Ashraf Ghani, and High Council for National Reconciliation Chairman Abdullah Abdullah at the White House June 25.

Sitting down with the pair of Afghan leaders, Biden shared an optimistic message.

"The partnership between Afghanistan and the United States is not ending. It’s going to be sustained. And, you know, our troops may be leaving, but support for Afghanistan is not ending, in terms of support and maintenance of their -- helping maintain their military, as well as economic and political support," Biden said.

But Biden grew visibly agitated Friday when reporters peppered him with questions about the future of Afghanistan.

"Look, we were in that war for 20 years, 20 years. And I think -- I met with the Afghan government here in the White House, in the Oval. I think they have the capacity to be able to sustain the government. There are going to have to be, down the road, more negotiations, I suspect," Biden said. "But I am -- I am concerned that they deal with the internal issues that they have to be able to generate the kind of support they need nationwide to maintain the government."

Prior to the Fourth of July weekend, Biden groused about continued questions on the deteriorating situation in Afghanistan.

"I want to talk about happy things, man," Biden said.

ABC News's Luis Martinez contributed reporting.