In light of the Taliban's rapid advance, Senate Republican minority leader Mitch McConnell has called on the US government to step up support for the Afghan security forces immediately. Unless President Joe Biden "changes course quickly, the Taliban are well on their way to securing a major military victory," warned McConnell. Biden had to promise more aid to the Afghan forces "immediately", including continued air support after the US troops withdrew on August 31, he demanded.

"If that doesn't happen, Al-Qaeda and the Taliban could celebrate the 20th anniversary of the September 11 terrorist attacks by burning down our embassy in Kabul," warned McConnell on, referring to groups of Islamic militants.

The announcement of the further reduction in the staff of the US embassy and the "hasty" relocation of additional troops to Afghanistan "appear like preparations for the fall of Kabul," said McConnell.

"A great embarrassment and a global crisis"

McConnell warned if the Taliban took power in Afghanistan and the terrorist organization Al-Qaeda returned there, it would boost Islamist extremists around the world. "President Biden's strategy turned an imperfect but stable situation into a great embarrassment and a global crisis within weeks," said the influential Republican angrily. The costs and consequences of Biden's actions would affect the world, he warned.

McConnell did not mention, however, that Biden's predecessor, Republican President Donald Trump, had agreed with the Taliban to withdraw all international troops by May 1.

Biden delayed the withdrawal of the 2,500 or so US soldiers who had remained in the spring, but adhered to the decision in principle.

The US military is expected to leave Afghanistan by the end of August.

The Taliban claimed to have taken the second largest city, Kandahar.

"Kandahar has been completely conquered," said a Taliban spokesman on Twitter on Friday.

"The mujahideen have reached Martyrs' Square in the city." A local resident told the AFP news agency that the Afghan army had apparently retreated.

Numerous soldiers went to a military facility outside the city.

On Thursday, the third largest Afghan city, Herat, fell into the hands of the Islamists.

In addition, the Taliban advanced on the capital Kabul and captured the provincial capital Ghazni, 150 kilometers southwest of Kabul.

The government forces have now lost control of most of the north and west of Afghanistan.

In addition to Kabul, the Afghan government only controls a handful of areas and besieged cities in many places.