Saleh, who resigned last week from his post, told this to 'The Sunday Times': "The ISI is part of the landscape of destruction in this country (Afghanistan), no doubt, so it will be a waste of time to provide evidence of ISI involvement. They are a part of it."
The paper said testimony by western and Afghan security officials, Taliban commanders, ex-Taliban ministers and a senior Taliban emissary show the extent to which the ISI "manipulates" the Taliban's strategy in Afghanistan.
It also referred to a report published by the London School of Economics (LSE) which summed up that "Pakistan appears to be playing a double-game of astonishing magnitude" in Afghanistan.
The report's author, Matt Waldman, a Harvard analyst, argued that previous studies significantly "underestimated" the influence that Pakistan's ISI exerts over the Taliban.
Far from being the work of rogue elements, interviews suggest this "support is official ISI policy", he said.
"The report is consistent with Pakistan's political history in which civilian leaders actively backed 'jihadi' groups that operate in Afghanistan and Kashmir," Waldman said.
Pakistani support for the Taliban is prolonging a conflict that has cost the West billions of dollars and hundreds of lives, the report said, noting that last week 32 NATO soldiers were killed.
The LSE report, based on dozens of interviews and corroborated by two senior western security officials, stated: "As the provider of sanctuary and substantial financial, military and logistical support to the insurgency, the ISI appears to have strong strategic and operational influence - reinforced by coercion.
"There is thus a strong case that the ISI orchestrates, sustains and shapes the overall insurgent campaign."
Mullah Abdul Ghani Baradar, the Taliban's former second in command, was arrested by the ISI earlier this year with seven other Taliban leaders.
Shortly after Baradar's arrest, the ISI captured two other Taliban members - Mullah Abdul Qayyum Zakir and his close associate and friend Mullah Abdul Rauf. Both men were released after just two nights in custody, the paper reported.
"To say the least, this is compelling evidence of significant ISI influence over the movement and it is highly likely that the release was on ISI terms or at least on the basis of a mutual understanding," the London School of Economics (LSE) report said.
The "promotions" of Zakir and Rauf will give Pakistan greater leverage over future peace talks, Taliban and western officials said.
The report quoting officials said, to ensure that the Pakistani government retains its influence over the Taliban's leadership, the ISI has placed its own representatives on the Quetta shura.
Up to seven of the Afghan Taliban leaders who sit on the 15-man shura are believed to be ISI agents. However, some sources maintain that every member of the shura has ISI links.
"It is impossible to be a member of the Quetta shura without membership of the ISI," said a senior Taliban intermediary who liaises with the Afghan government and Taliban leaders.
The LSE report said: "Interviews strongly suggest that the ISI has representatives on the shura, either as participants or observers, and the agency is thus involved at the highest levels of the movement."
The two shura members who receive the strongest support from the ISI are Taib Agha, former spokesman for Mullah Omar, the Taliban supreme leader, and Mullah Hasan Rahmani, the former Taliban governor of Kandahar, according to the Taliban intermediary and western officials.
Strategies that the ISI encourages, according to Taliban commanders, include: cutting NATO's supply lines by bombing bridges and roads, attacking key infrastructure projects, assassinating pro-government tribal elders, murdering doctors and teachers, closing schools and attacking school girls.
ISI agents hand chits to Taliban commanders who use them to buy weapons at arms dumps in North Waziristan, the report claimed.
The Taliban's "plastic bombs" - the low metal content improvised explosive devices (IEDS) that kill the majority of British soldiers who die in Afghanistan - were introduced to the Taliban by Pakistani officials, according to Taliban commanders, the Taliban intermediary and western officials.
The materials allow Taliban sappers to plant bombs that can evade NATO mine detectors.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.