In an op-ed published Wednesday in The Washington Post, Ahmad Massoud said "America can still be a great arsenal of democracy" by supporting his fighters.

"I write from the Panjshir Valley today, ready to follow in my father's footsteps, with mujahideen fighters who are prepared to once again take on the Taliban," he said.

His father Ahmad Shah Massoud, known as the Lion of Panjshir, led the strongest resistance against the Taliban from his stronghold in the valley northeast of Kabul until his assassination in 2001.

Famed for its natural defences, the redoubt tucked into the Hindu Kush mountains never fell to the Taliban during the civil war of the 1990s, nor was it conquered by the Soviets a decade earlier, and is now Afghanistan's last remaining holdout.

Hoping to follow in his "father's footsteps", Massoud said he has been joined by former members of the country's special forces and soldiers from the Afghan army "disgusted by the surrender of their commanders".

Social media images show Afghanistan's defiant vice president Amrullah Saleh meeting with Massoud, and the duo appear to be assembling the first pieces of a guerrilla movement to take on the Taliban.

"But we need more weapons, more ammunition and more supplies," Massoud said.

- 'Ground zero' -

Tens of thousands of people have tried to flee Afghanistan since the hardline Islamist militants swept into the capital on Sunday, completing a stunning rout of government forces and ending two decades of war.

Nearly 6,000 people -- including US citizens and Afghans -- have been evacuated by the US military, with the government urging the Taliban to allow safe passage for people to flee.

Massoud said the Taliban poses a threat beyond Afghanistan's borders.

"Under Taliban control, Afghanistan will without doubt become ground zero of radical Islamist terrorism; plots against democracies will be hatched here once again."

Massoud said his fighters are ready for the coming conflict, but need American assistance.

Since their takeover, the Taliban have been showing off the huge stash of weapons, equipment and munitions they have seized from Afghan forces -- most of it supplied by the United States.

Social media images showed Taliban fighters carrying M4 and M18 assault rifles, M24 sniper weapons, and driving around in the iconic US Humvees.

The seizures have heightened criticism of President Joe Biden's hasty withdrawal.

Massoud said that, after 20 years, the US and Afghanistan have shared "ideals and struggles" and he asked Washington to continue supporting the "cause of freedom" rather than abandon Afghans to the Taliban.

"You are our only remaining hope," he said.