Branded as a "veritable arm" of ISI, the Haqqani network's operational chief Sirajuddin Haqqani has claimed that his group did not kill Burhanuddin Rabbani and denied any links with the Pakistani spy agency.
"We haven't killed Burhanuddin Rabbani and this has been said many times by the spokespersons of the Islamic Emirate," Sirajuddin Haqqani told BBC in an interview, his first public utterances in years.
Sirajuddin also said his network, blamed by US military officials for a string of high-profile attacks on American interests in Afghanistan, was not linked to Pakistan's ISI.
Former US military chief Admiral Mike Mullen had branded Haqqani network as a "veritable arm" of ISI, used by the spy agency to wage a proxy war in Afghanistan.
But the Haqqani network chief said that the 'Islamic Emirate', the name given to the Taliban government when they assumed power in Afghanistan in 1996, was behind "the attack on US embassy, Nato headquarters and other attacks in Kabul, which he said were ordered by a military council of Taliban.
Vowing what he called the "game being played by the West... is close to an end", Sirajuddin said: "in every operation we get the order, planning and financial resources from the Emirate's leadership and we act accordingly."
He pledged loyalty to Taliban chief Mullah Omar, saying "he is our leader and we totally obey him."
Afghan officials have blamed Taliban for the September 20 assassination of Rabbani by a turban bomber, saying the killer was a Pakistani and the plot had been hatched in Quetta in Balochistan, where top Taliban council is based.
Haqqani said during the Soviet occupation of Afghanistan in the 1980s, the mujahideen "had contacts with the intelligence agencies of Pakistan and other countries, but after the invasion (of Afghanistan) by the Americans there have never been contacts by intelligence agencies of other countries which could be effective for us".
He said accusations of links to the ISI were an attempt "to hide their (US) failure and to confuse peoples' minds".
BBC did not give out the location of the interview, whether it was in Afghanistan or tribal areas of Pakistan. But said security consideration ruled out a face to face interview in which the answers could be challenged.
It said the questions were delivered through an intermediary who returned with the audio response. "BBC understands that the audio response is genuine."
In the interview, Siraj had a message to the "government and people" of Pakistan, telling them to be careful of their Islamic values. "They should understand that the American will not let Pakistan live a peaceful life until he destroys all the wealth and values of it."
Sirajuddin is the eldest son of group's founder Jalaluddin Haqqani who led the outfit in the war against Soviet. The son now runs the group, which is believed to have around 8,000-13,000 well-armed fighters.
BBC quoted a senior Afghan intelligence official as rejecting the Haqqani's denial of links to the ISI, saying that the network was ISI's creation. "The ISI gives the network intelligence, tactical advice and training. Groups like Lashkar-e Taiba give fighters and share information and experience about battles," the official told the BBC.
"We know for sure that Lashkar-e Taiba fighters come and fight alongside the Haqqani network. The Haqqanis fight alongside Lashkar-e Taiba in Kashmir. They have a long-standing relationship."