A senior member of the Haqqani militant network which is seen as one of the biggest threats to US-led forces in Afghanistan has been shot dead in the Pakistani capital, the Taliban said Monday.

Unidentified gunmen attacked Nasiruddin Haqqani, the group's chief fundraiser and son of its founder, on the edge of Islamabad on Sunday evening, the militants told AFP.

The Haqqanis have been blamed for spectacular attacks on Afghan government and NATO targets across Afghanistan as well as for kidnappings and murders.

The killing comes just over a week after a US drone strike killed Pakistani Taliban chief Hakimullah Mehsud in North Waziristan tribal district.

Washington holds the Haqqanis responsible for some of the most high-profile attacks in Afghanistan, including a 2011 siege of the US embassy and, in 2009, the deadliest attack on the CIA in 25 years.

"I can confirm that Nasiruddin Haqqani, 36, was shot dead in Islamabad's Bhara Kahu area on Sunday night. At least four gunmen opened fire on him," a senior Afghan Taliban source from the Haqqani network told AFP.

Haqqani's body has been taken to Miranshah, the main town of North Waziristan, for burial, the source said.

A spokesman for the Pakistani Taliban confirmed the death and vowed to take revenge, accusing Pakistan's Inter-Services Intelligence (ISI) agency of killing him.

"Nasiruddin Haqqani has been martyred by ISI," Shahidullah Shahid, the main spokesman for the Tehreek-e-Taliban Pakistan (TTP), told AFP.

"He was killed because he bravely supported Taliban chief Hakimullah Mehsud."

Afghanistan's NDS spy agency also confirmed Haqqani's death but blamed it on an "internal conflict". It did not give further details.

The United States put the Haqqani network on its terror blacklist in September 2012 and the Pentagon said the group represented a "significant threat" to national security.

The UN followed up with global sanctions on the network two months later, saying in its designation that the group was linked to Al-Qaeda, the Islamic Movement of Uzbekistan and a string of militant groups in Pakistan including the TTP.

The Haqqanis have been a source of friction in US-Pakistan relations. The outgoing top US military officer, Admiral Mike Mullen, in 2011 called the group a "veritable arm" of the ISI.

The Haqqani network was founded by Nasirudddin's father Jalaluddin Haqqani -- a disciplined Afghan guerrilla leader bankrolled by the United States to fight Soviet troops in Afghanistan in the 1980s. He is now based with his family in Pakistan.

In the 1980s Jalaluddin was close to the CIA and Pakistani intelligence. He allied himself to the Taliban after they took power in Kabul in 1996, serving as a cabinet minister under the militia's supreme leader, Mullah Omar.

When American troops arrived after the 9/11 attacks Haqqani sought refuge in North Waziristan and became one of the first anti-US commanders based in Pakistan's border areas.

He has training bases in eastern Afghanistan and is close to Al-Qaeda. His fighters are active across east and southeast Afghanistan and in the capital Kabul.

The network is militarily the most capable of the Afghan Taliban factions. It operates independently but remains loyal to Mullah Omar.

Jalaluddin is now in his late 70s and frail. His seat on the Afghan Taliban leadership council has passed to another son Sirajuddin, who effectively runs a fighting force of at least 2,000 men.