A Taliban fighter stands guard on a street in Herat on August 14. Photo: AFP

Taliban fighters on Saturday captured the key northern Afghan city of Mazar-i-Sharif and closed in on Kabul, as US President Joe Biden sent more troops to evacuate American personnel and their allies.

Just before residents confirmed the fall of Mazar-i-Sharif, once an anti-Taliban bastion, beleaguered Afghan President Ashraf Ghani addressed the nation, vowing to prevent further bloodshed, despite the rout suffered by Afghan forces over the last 10 days.

But Ghani – who went to Mazar-i-Sharif just days ago to rally his faltering troops – gave no hint in his speech that he would take responsibility for the calamitous military collapse or resign.

Kabul has effectively become the besieged last stand for government forces, who have offered little or no resistance elsewhere.

Insurgent fighters are now camped just 50 kilometres from the capital, with the United States and other countries scrambling to airlift their nationals to safety ahead of a feared all-out assault.

Taliban fighters stand guard in front of the provincial governor’s office in Herat on August 14. Photo: AFP

As a new wave of US military personnel landed to oversee the evacuation of embassy employees and thousands of Afghans who worked for US forces and now fear Taliban reprisals, Biden said more soldiers would follow.

“I have authorized the deployment of approximately 5,000 US troops” to oversee both the evacuations and the final withdrawal of US forces after 20 years on the ground, Biden said after meeting with his national security team.

That represented an influx of 1,000 troops, from the roughly 1,000 already on the ground, and 3,000 soldiers ordered in a few days ago, a US defense official said.

“I was the fourth president to preside over an American troop presence in Afghanistan – two Republicans, two Democrats. I would not, and will not, pass this war on to a fifth,” Biden said.