U.S. President Joe Biden said on Thursday that the U.S. military mission in Afghanistan will conclude on August 31, days ahead of his original September 11 deadline.

"In this context, speed is safety," Biden said in his remarks at the White House. "Conducting our drawdown differently would have certainly come with an increased risk of safety to our personnel."

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The president in April ordered all U.S. troops to leave Afghanistan before September 11, the 20th anniversary of the terrorist attacks that drew the United States into its longest war.

In defending the withdrawal, he said that the U.S. military had achieved its counterterrorism objectives in the 20-year war. 

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

He reaffirmed that the United States will continue providing support to the Afghan government and planned to move Afghan nationals who worked with U.S. forces out of the country to wait for their U.S. visa to be processed. 

"Starting this month, we're going to begin relocation flights for Afghanistan SIV (Special Immigrants Visa) applicants and their families who choose to leave," he said. 

The Wall Street Journal last month reported that the U.S. intelligence community assessed that the Afghan government could collapse within six months after the complete withdrawal of the U.S. military. 

Biden rejected the collapse scenario on Thursday. "They didn't reach that conclusion," he told reporters, saying he had confidence in the capacity of the Afghan troops. 

Johnson: Most UK troops now out

British Prime Minister Boris Johnson announced on Thursday the withdrawal of all British troops from Afghanistan, signaling the end of the UK's military mission in the conflict. 

"All British troops assigned to NATO's mission in Afghanistan are now returning home," Johnson told parliament, praising what British forces had achieved while at the same time acknowledging the "perils" facing Afghanistan. 

The prime minister would not disclose the exact timetable of the departure for security reasons, but added that most of the 750 remaining British troops had already left. 

He demanded that the Taliban abide by their commitments to a peace deal signed last year. 

"I am sure they will be aware there is no military path to victory for the Taliban," he said. "There must be a peaceful and a negotiated settlement for the political crisis." 

Johnson added he did not underestimate the challenges facing Afghanistan, saying the government would continue to provide development assistance.

British forces were first deployed to Afghanistan in 2001 following the September 11 attacks on the United States and played a major role in combat operations until 2014. 

Over the last two decades, 150,000 members of Britain's armed forces served in Afghanistan. A total of 457 British soldiers were killed in the country. 

Civil war warning

The head of Britain's armed forces warned on Thursday that there was a possibility that Afghanistan could be on a path to civil war as U.S. and other foreign troops leave. 

Chief of the Defence Staff Nick Carter, speaking after it was announced most British soldiers have left Afghanistan, said it was "plausible" that the country would collapse without international forces there. 

Afghanistan could see a situation like the country's 1990s civil war "where you would see a culture of warlordism and you might see some of the important institutions like security forces fracturing along ethnic, or for that matter, tribal lines," Carter said. 

"If that were to happen, I guess the Taliban would control part of the country. But, of course, they would not control all of the country."

Fighting raged on Thursday between the Taliban and government forces in the northwestern province of Badghis, the first provincial capital to face an all-out assault by the Taliban since the U.S. stepped up its troop withdrawal. The government in Kabul responded by flying hundreds of commandos into the area.

Over 2,400 U.S. troops have been killed in Afghanistan over the past two decades, with 20,000 wounded, according to the Pentagon. 

Estimates show that over 66,000 Afghan troops have been killed, and over 2.7 million people have had to leave their homes. 

(With input from agencies)

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