A Taliban ambush on Afghan Vice-President Abdul Rashid Dostum's convoy backfired on Friday when the war-hardened leader's men fought back, killing at least four militants and capturing a dozen more on a remote highway.

Dostum, an ethnic Uzbek who led a personal army fighting the Taliban regime before the 2001 U.S. military intervention and who is accused by rights groups of involvement in war crimes, joined the political mainstream last year as President Ashraf Ghani's running mate.

He traded the new suit for a military uniform last month to accompany the army and armed villagers fighting an offensive by the Islamists in his northern heartland.

Dostum's armoured vehicle was moving in a convoy along a remote highway in the province of Faryab when 20 militants opened fire, said police chief Subhan Qul, who was in the convoy. Dostum's vehicle was hit several times by shots in the gunfight that followed, Afghan media reported.

"As a result of almost three hours of fighting at least four Taliban are killed and 13 are captured alive," an official from Dostum's media office said. Earlier a spokesman said eight militants died. There were no initial reports of casualties among the security forces.

Afghan forces are largely fighting the Taliban alone for the first time this year after all but a rump of foreign coalition soldiers left the country last year. The insurgents have made advances in the north and south but struggled to hold territory.

Dostum has been itching to take the fight to the Taliban for months, but has had to tread carefully because of concerns by Ghani that his return to the front lines would drag Afghanistan back into the chaos of the 1990s when militias waged civil war.

Dostum helped end Taliban rule at the start of the U.S. invasion but was accused by rights groups at the time of deliberately killing up to 2,000 Taliban prisoners in shipping containers. He denies this.

U.S.-led forces have spent $54 billion training a national Afghan army and police for a unified fight against the Taliban insurgents but many power brokers dating back decades retain personal bodyguard units and often arsenals.

Since Ghani forbade him from taking what Dostum said were his 9,000 armed men into battle, he has instead toured Faryab with local soldiers and police, boosting morale and claiming to have helped clear swathes of territory from the Taliban's grip.

"Whether I command or don't command, my presence will get things done," the burly, moustachioed commander known by everyone as General Dostum said in a rare meeting with reporters in July.

"My presence will be felt. The police, the army know this very well. You will see - even the women will be throwing rocks at the Taliban," he said, seated in a padded armchair at his pink-painted compound.

* 20 militants attack Dostum's convoy -police chief

* Dostum's men fight back, kill 4 Taliban, capture 13

* No casualties among his security forces reported

* Dostum has spent weeks on northern front line with army

* President has not allowed him to revive fighting force