KABUL: The Taliban were in control of six Afghan provincial capitals on Tuesday after a blitz across the north that forced tens of thousands of people to flee their homes for the relative safety of Kabul and other centres.

The insurgents now have their eyes on Mazar-i-Sharif, the biggest city in the north, whose fall would signal the total collapse of government control in a region that has traditionally been anti-Taliban.

Government forces are also battling the hardline Islamists in Kandahar and Helmand, the southern Pashto-speaking provinces from where the Taliban draw their strength.

The United States - due to complete a troop withdrawal at the end of the month and end its longest war - has all but left the battlefield. However, its special envoy Zalmay Khalilzad has been sent to Qatar to try and convince the Taliban to accept a ceasefire.

Khalilzad "will press the Taliban to stop their military offensive", the State Department said, and "help formulate a joint international response to the rapidly deteriorating situation".

Officials from Afghanistan's most vested neighbours - Pakistan, China and Iran - would also attend meetings there.

But Pentagon spokesman John Kirby said it was down to the Afghan government and its forces to turn the tide, saying there was "not much" the United States could do to help.

Michael Kugelman, at the Woodrow Wilson International Center for Scholars, doubted Washington had the means to anything.

"I fear that the Taliban (are) just so strong and the Afghan military is so beleaguered right now, it's going to be hard to find some type of momentum-changer from the US," he said.

The Taliban have appeared largely indifferent to peace overtures, and seem intent on a military victory to crown a return to power after their ouster 20 years ago in the wake of the September 11 attacks. As fighting raged, tens of thousands of people were on the move inside the country, with families fleeing newly captured Taliban cities with tales of brutal treatment at the hands of the insurgents.

"The Taliban are beating and looting," said Rahima, now camped out with hundreds of families at a park in the capital Kabul after fleeing Sheberghan province.

"If there is a young girl or a widow in a family, they forcibly take them. We fled to protect our honour."

"We are so exhausted," added Farid, an evacuee from Kunduz who did not want to be further identified.