The United States and Britain ordered Friday the deployment of thousands of troops to Afghanistan to evacuate their nationals, as the Taliban overran more key regional cities in an offensive that has left the capital dangerously exposed.

The Western forces' announcements of rushed extractions came as the Taliban claimed they had taken control of Kandahar, the nation's second biggest city in Taliban heartland, and Lashkar Gah leaving only Kabul and pockets of other territories in government hands.

"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The claim was backed up by a resident, who told AFP government forces appeared to have withdrawn en masse to a military facility outside the southern city.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 Taliban have also captured the key southern city of Lashkar Gah, a senior Afghan security source told AFP on Friday, confirming a claim by the insurgents. Military and government officials had evacuated the city after striking a deal with the militants, the security source told AFP.

The Afghan government has now effectively lost control of most of the country, following an eight-day blitz into urban centres by the Taliban that has left the Afghan government and its US backers stunned.

The offensive was launched after the United States and its allies all but withdrew its forces from Afghanistan, with President Joe Biden determined to end two decades of war by September 11.

- No regrets -

Biden has insisted he has no regrets with his decision, but the speed and ease of the Taliban's urban victories in recent days has been a surprise and forced new calculations.

Washington and London announced on Thursday night moves 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."

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.

Britain's Defence Secretary Ben Wallace said London would send 600 of its own troops to evacuate its nationals and former Afghan staff.

Price said the United States would also start sending in daily flights to evacuate Afghan interpreters and others who assisted the Americans.

- 'Laid down their arms' -

The conflict has escalated dramatically since May, when US-led forces began the final stage of their troop withdrawal.

After months of taking what were considered less strategically important rural areas, the Taliban zeroed in on the cities.

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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.

Pro-Taliban social media accounts have boasted of the vast spoils of war their fighters had recovered in recent days.

They have posted photos of armoured vehicles, heavy weapons and even a drone seized by the insurgents at abandoned military bases.

After being under siege for weeks, government forces on Thursday pulled out of Herat -- an ancient silk road city near the Iranian border -- and retreated to a district army barracks.

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."

On Thursday, 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.

A security source told AFP that Qala-i-Naw, capital of Badghis province in the northwest, also capitulated on Thursday. 

- 'A predictable disaster' -

As the rout unravelled, three days of meetings between key international players on Afghanistan wrapped in Qatar without significant progress Thursday.

See Also: Peace in Afghanistan means peace in Pakistan, COAS tells EU envoys

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 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 on Thursday for his "reckless policy."

"Afghanistan is careening toward a massive, predictable, and preventable disaster," Senator Mitch McConnell said in a statement.

Biden's 'reckless' Afghan policy leading to disaster: Top Republican

The top Republican in Congress blasted President Joe Biden Thursday for his "reckless policy" on Afghanistan, as the United States moved to evacuate embassy workers ahead of the Taliban advance.

"Afghanistan is careening toward a massive, predictable, and preventable disaster," Senator Mitch McConnell said in a statement.

"The Biden administration has reduced US officials to pleading with Islamic extremists to spare our embassy as they prepare to overrun Kabul," he said.

McConnell's broadside, the strongest criticism yet by a senior official, came after the administration announced it was sending 3,000 troops to secure Kabul's international airport for a series of evacuation flights for US embassy staff and Afghans who worked for US forces.

The announcement heightened the perception that after 20 years of war the United States is abandoning the country as the Taliban insurgents claim control of city after city and increasingly threaten the Washington-backed government in Kabul.

McConnell said Biden should step up military support for the Afghan forces rather than complete the withdrawal he set for August 31.

"President Biden's strategy has turned an imperfect but stable situation into a major embarrassment and a global emergency in a matter of weeks," he said.

"If we let the Taliban dominate Afghanistan and Al-Qaeda return, it will resonate throughout the global jihadist movement."

McConnell said the decision to deploy US troops to manage the evacuation "seem(s) like preparations for the fall of Kabul," which he compared to "the humiliating fall of Saigon in 1975," when North Vietnamese troops seized control of the city two years after the US military withdrew.