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Withdrawing from could cause a collapse of the country's government in as little as six months, US officials said, as concerns grow over the spread of forces and the captureÌýof a key government crossing.

A new assessment of the situation in Afghanistan by the US intelligence community, which hasn’t yet been reported, falls in line with estimations made by the US military, who have been saying that total withdrawal will leave a vacuumÌýthat will be filled by the Taliban, according to sources who spoke to The Wall Street Journal.

Initial estimates by US said the Afghanistan government could hold out for two years after US withdrawal, and the updated timeline shows that the Taliban’s recent gains are significant.

The military has already withdrawn 1,750 troops – half of its 3,500 numbers – and its equipment, with total withdrawal set to be completed by 11 September, US President Joe Biden revealed.

"It is a dynamic situation,"ÌýPentagon press secretary John Kirby said earlier this week.

"If there need to be changes made to the pace or to the scope and scale of the retrograde on any given day or in any given week, we want to maintain the flexibility to do that."

Earlier this week the Taliban captured Afghanistan's main border crossing with Tajikistan, with some security forces abandoning their posts and fleeing across the frontier.

The seizure of Shir Khan Bandar, in the far north of Afghanistan about 50 kilometres (30 miles) from Kunduz city, is the most significant gain for the Taliban since they stepped up operations on 1 May when the US began the final stages of its troop withdrawal.

The United States called Tuesday for an end to violence in Afghanistan, blaming Taliban insurgents for much of the bloodshed, three days ahead of a visit by President Ashraf Ghani to the White House.

"We urge the sides to engage in serious negotiations that determine a political roadmap for Afghanistan's future," State Department spokesman Ned Price told reporters.

"We continue to call for an end to the ongoing violence that has been driven largely by the Taliban," Price said.

On Friday, President Joe Biden will meet with Ghani and with Abdullah Abdullah, who is overseeing the government side in the peace talks with the Taliban.