A key leader of the Afghan militant group, the Haqqani network, has told the BBC it was not responsible for killing Burhanuddin Rabbani, the man overseeing Taliban peace talks.
Afghan officials have blamed the Taliban-affiliated network for the suicide attack on Rabbani.
Siraj Haqqani also told BBC Pashto his network was not linked to Pakistan's spy agency, the ISI.
Mr Haqqani was giving an audio response to written questions from the BBC.
Security considerations ruled out a face-to-face interview in which the answers could be challenged, but the BBC understands that the audio response is genuine.
The questions were delivered through an intermediary, who returned with the audio response.
Siraj Haqqani is the son of group founder Jalaluddin Haqqani and has a key role in its operations.
The Haqqanis have been blamed for a series of deadly recent attacks in Kabul.
Burhanuddin Rabbani was killed at his home in Kabul on 20 September when meeting a man who said he was carrying an important peace message from the Taliban. The man detonated a bomb hidden in his turban.
In his interview response, Siraj Haqqani simply says: "We haven't killed Burhanuddin Rabbani and this has been said many times by the spokespersons of the Islamic Emirate."
The Islamic Emirate is the name the Taliban gave to Afghanistan when they took control in 1996.
The Taliban have said they do not wish to comment on the Rabbani killing.
Afghan investigators say the killer was a Pakistani and that the murder was plotted in the Pakistani city of Quetta.
Afghan government officials have also accused the Pakistan intelligence agency, the ISI, of involvement, a charge Islamabad denies. Afghanistan and the US have both accused the ISI of links to the Haqqani network.
Mr Haqqani said the "Islamic Emirate" was behind "the attack on the US embassy, Nato headquarters and other attacks" in Kabul, which he said were ordered by a "military council" and were not the work of individuals.
ISI links denied
In relation to links to the ISI, Mr Haqqani said that during the Soviet occupation of the 1980s, mujahideen fighters "had contacts with the intelligence agencies of Pakistan and other countries, but after the invasion by the Americans there have never been contacts by intelligence agencies of other countries which could be effective for us".
He said the Haqqanis "have been contacted and are being contacted by intelligence agencies of many Islamic and non-Islamic countries, including the US, asking us to leave the sacred jihad and take an important part in the current government".
Mr Haqqani said that was not his network's responsibility, but he added: "We know that their aim is not peace, they want to create tension among the Emirate's mujahideen."
He said accusations of links to the ISI were an attempt "to hide their failure and to confuse peoples' minds".
A senior Afghan intelligence official rejected the Haqqanis' denial of links to the ISI, saying the group was the ISI's creation.
"The ISI gives the network intelligence, tactical advice and training. Groups like Lashkar-e Taiba give [the network] 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 longstanding relationship."
Analysts say the Haqqanis' denial of an ISI connection works to Islamabad's advantage, which has been under pressure from the US because of its ties to the militants.
"Pakistan fears the US, so Siraj [Haqqani] is giving an interview to change public perception about its ties to the ISI," political analyst Haroun Mir told the BBC.
If the Haqqanis were in contact with the Americans, this would be via Pakistan, said author and analyst Ahmed Rashid.
"The [US] mood has changed against the Haqqanis... It is not that the talks with the Haqqanis are like the talks with the mainstream Taliban, which I think are genuine and more constructive talks, " he told the BBC.
"There are probably contacts with the Pakistanis acting as a liaison."
Mr Haqqani vowed that "the game which is being played by the West... is close to an end".
He pledged loyalty to Mullah Omar, saying he "is our leader and we totally obey him".
"In every operation we get the order, planning and financial resources from the Emirate's leadership and we act accordingly," Mr Haqqani said.
He also delivered a message to the "government and people of Pakistan", telling them to be "careful of their Islamic values. They should understand that America will not let Pakistan live a peaceful life until it destroys all the wealth and values of it."
After Rabbani's death, Afghan President Hamid Karzai said his government would no longer hold peace talks with the Taliban, but would instead focus on dialogue with Pakistan.
Mr Karzai said: "[Taliban leader] Mullah Omar doesn't have an address... their peace emissary turns out to be a killer, whom should we talk to?
"The Afghan nation asks me who's the other party that you hold talks with? My answer is, Pakistan."