The US announcement came hours before a Taliban spokesman tweeted the fall of Kandahar - the movement’s spiritual birthplace and the scene of days of fierce fighting.
“Kandahar is completely conquered. The Mujahideen reached Martyrs’ Square,” a Taliban spokesman tweeted on an officially recognised account, referring to a city landmark.
The claim was backed up by a resident, who told AFP government forces appeared to have withdrawn en masse to a military facility outside the southern city.
The government has now effectively lost control of most of the country, following an eight-day onslaught by the Taliban that has caught the United States by surprise, even as it pushes forward with a troop withdrawal due to be completed by the end of the month.
As the insurgents swept across more territory, Washington and London moved to quickly pull out their embassy staff and other citizens from the capital.
“We are further reducing our civilian footprint in Kabul in light of the evolving security situation,” US State Department spokesman Ned Price told reporters, while noting the embassy would remain open.
“This is not abandonment. This is not an evacuation. This is not the wholesale withdrawal,” he said.
The Pentagon said 3,000 US troops would be deployed to Kabul within the next 24 to 48 hours, underscoring that they would not be used to launch attacks against the Taliban.
UK Defence Secretary Ben Wallace said London would send 600 of its own troops to evacuate its nationals and “support the relocation of former Afghan staff who risked their lives serving alongside us”.
Price said the United States would also start sending in daily flights to evacuate Afghan interpreters and others who assisted the Americans and are fearful for their lives due to the Taliban’s sweeping offensive.
After being under siege for weeks, government forces yesterday pulled out of Herat - an ancient silk road city near the Iranian border - and retreated to a district army barracks.
“We had to leave the city in order to prevent further destruction,” a senior security source from the city told AFP.
A Taliban spokesman, however, tweeted that “soldiers laid down their arms and joined the Mujahideen”.
Herat resident Masoom Jan told AFP the city’s fall had been abrupt, saying the Taliban “entered the city in rush. They raised their flags in every corner.”
Yesterday, the interior ministry also confirmed the fall of Ghazni, about 150 kilometres (95 miles) from Kabul and along the major highway to Kandahar and the Taliban heartlands in the south.
“The enemy took control,” spokesman Mirwais Stanikzai said in a message to media, adding later the city’s governor had been arrested by Afghan security forces.
Pro-Taliban Twitter feeds showed a video of him being escorted out of Ghazni by Taliban fighters and sent on his way in a convoy, prompting speculation in the capital that the government was angered with how easily the provincial administration capitulated.
A security source told AFP that Qala-i-Naw, capital of Badghis province in the northwest, also capitulated yesterday.
As the rout unravelled, three days of meetings between key international players on Afghanistan wrapped in Qatar without significant progress yesterday.
In a joint statement, the international community, including the United States, Pakistan, the European Union and China, said they would not recognise any government in Afghanistan “imposed through the use of military force”.
Price called for a negotiated solution and reiterated US President Joe Biden’s frustration at the deteriorating situation, saying Afghan government forces outnumbered the Taliban by more than three to one after billions of dollars of US support over two decades.
Facing pressure at home, Biden was blasted by the top Republican in Congress yesterday for his “reckless policy”.
“Afghanistan is careening toward a massive, predictable, and preventable disaster,” Senator Mitch McConnell said in a statement.
The conflict has escalated dramatically since May, when US-led forces began the final stage of a troop withdrawal due to end later this month following a 20-year occupation.
Pro-Taliban social media accounts also boasted of the vast spoils of war their fighters had recovered in recent days, posting photos of armoured vehicles, heavy weapons and even a drone seized by the insurgents at abandoned military bases.
In the past week, the insurgents have taken over a dozen provincial capitals and encircled the biggest city in the north, the traditional anti-Taliban bastion of Mazar-i-Sharif, which is now one of the few holdouts remaining.
Fighting was also raging in Lashkar Gah - another pro-Taliban heartland in the south.
Late yesterday, a security source told AFP government forces there were also considering evacuating to nearby Camp Bastion, one of the largest US bases in the country.
Hundreds of thousands have been displaced by the fighting that has enveloped the country.
In recent days, Kabul has been swamped by the displaced, who have begun camping out in parks and other public spaces, sparking a fresh humanitarian crisis in the already overtaxed capital.