A militant commander who was believed to have defected to Isisfrom the Taliban was among six people killed in a drone strike in Afghanistan, Afghan officials have claimed.

The Afghan military reported in January that former Guantanamo Bay detainee Mullah Abdul Rauf swore allegiance to Isis and was establishing a network of followers, who were in turn recruiting people to join them across the southern Helmand province.

He was allegedly killed in the southern Helmand province on Monday when the car he was travelling in was hit by a drone. His brother-in-law is believed to be among the casualties.

Rauf was understood to be a former Taliban commander who was arrested after the fall of the Taliban in the US-led invasion. He has been influential in Afghanistan’s jihadi movement for well over a decade, according to the Associated Press.

Afghanistan’s main intelligence agency, the National Directorate of Security (NDS), said Rauf was in charge of Isis across southwestern Afghanistan and died just before midday after a “successful operation”.

A military document leaked by WikiLeaks had him listed as a Guantanamo Bay inmate who was “associated with several Taliban commanders and leaders in Afghanistan”.

The document said Rauf, who was captured by US forces in 2001, had claimed to be a Taliban foot soldier and bread deliverer and denied having ever been promoted within its ranks.

He was deemed to be of medium intelligence value by the US because of his possible knowledge of Taliban leadership and command. Rauf had denied having any links to senior leadership but the US dismissed this as implausible because he served three tours with the Taliban.

He was suspected of falling out with the Taliban leader Mullah Omar before his suspected defection.

His death has not yet been confirmed by Nato sources.