LASHKAR GAH: A missile-firing drone killed six people in Afghanistan on Monday including a veteran militant believed to have defected to Islamic State (IS) from the Taliban, Afghan officials said.

The senior militant, former Guantanamo Bay detainee Mullah Abdul Rauf, was killed in the violence-plagued southern province of Helmand, officials there said.

Police chief Nabi Jan Mullahkhel said Rauf was travelling in a car when the drone attacked. The other casualties included his brother-in-law and four Pakistanis, Mullahkhel said.

He did not give more details of the attack. The United States operates drones over Afghanistan and neighbouring Pakistan. U.S.-led forces in Afghanistan did not immediately respond to requests for comment.

Rauf had been influential in Afghanistan's jihadi movement for well over a decade.

Media reports last month said he had begun recruiting for Islamic State, part of a push by the movement to gain traction beyond its stronghold in Iraq and Syria.

Read also: ‘IS active in Helmand’

Afghanistan's main intelligence agency, the National Directorate of Security (NDS), said in a statement Rauf was in charge of IS in southwestern Afghanistan and he was killed just after mid-day in “a successful military operation”.

Helmand's deputy governor, Mohammad Jan Rasulyar, said Rauf's membership of IS could not be confirmed but his associates were dressed in black outfits often worn by IS members.

“It is too early to confirm that he was Daish but his people were wearing the same clothes and mask,” Rasulyar said, referring to IS.

A U.S. military report released by the anti-secrecy group WikiLeaks in 2011 said that Rauf had tried to pass himself off as a low level Taliban worker who “delivered bread,” but that interrogators suspected he was more senior.

Also in 2011, Newsweek magazine reported that Rauf had once led an elite fighting force close to Taliban leader Mullah Omar, and that after his return to Afghanistan in 2007 he had become the Taliban's shadow governor in Uruzgan province.

Earlier in January, an online video was released showing former militants of the Tehreek-i-Taliban (TTP) pledging allegiance to the Islamic State group.

Read more: Ex-TTP members pledge allegiance to Islamic State

At the end of the video, the militants killed a man they claim to be a Pakistani soldier.

The video raised concerns about whether IS has found support in Pakistan and Afghanistan, a region already awash with dozens of militant groups.

Taliban militants in Afghanistan and Pakistan owe their allegiance to Mullah Omar, a cleric who has led the Taliban since the 1990s and hasn't been publicly heard from for years.