NATO Secretary General Jens Stoltenberg said on Friday the alliance would keep its civilian diplomatic presence in Afghanistan as it tries to support the Afghan government and security forces in the face of the Taliban's offensive. 

"Our aim remains to support the Afghan government and security forces as much as possible. The security of our personnel is paramount. NATO will maintain our diplomatic presence in Kabul, and continue to adjust as necessary," Stoltenberg said, in a statement following a meeting of NATO envoys.

The Taliban has overrun a string of regional capitals in a lightning offensive since NATO troops largely pulled out of the country on the back of US President Joe Biden's decision to withdraw. 

Leading NATO powers, the US and Britain late on Thursday said they were ordering the deployment of thousands of troops back to Afghanistan to evacuate their citizens. 

"NATO Allies are deeply concerned about the high levels of violence caused by the Taliban's offensive, including attacks on civilians, targeted killings, and reports of other serious human rights abuses," Stoltenberg said. 

"The Taliban need to understand that they will not be recognised by the international community if they take the country by force. We remain committed to supporting a political solution to the conflict," the statement said. 

Diplomats at NATO painted a grim picture of the events unfolding in Afghanistan, with one likening them to the fall of Saigon at the end of the Vietnam War. 

"The situation is catastrophic," another diplomat told AFP. 

Washington and London announced plans late Thursday to quickly pull out their embassy staff and other citizens from the capital.

NATO allies Denmark and Norway announced Friday that they were temporarily shutting their Kabul embassies. 

The moves came as the insurgents took control of Kandahar, the nation's second biggest city, leaving only the capital Kabul and pockets of other territory in government hands. 

The government has now effectively lost control of most of the country, following an eight-day blitz into urban centres by the Taliban that has also stunned Kabul's Western backers.

The insurgents have taken over more than a dozen provincial capitals in the past week 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.