The Inter-Services Intelligence agency "conclusively authenticated" the delivery of a secret memorandum purportedly sent by Pakistan's civilian leadership to the former US military chief before army chief Gen Ashfaq Parvez Kayani raised the matter with President Asif Ali Zardari.
An ISI official flew to Europe and met Mansoor Ijaz, the Pakistani-American businessman who sent the memo to Admiral Mike Mullen through an intermediary, to ascertain the authenticity of the evidence that Ijaz claims to have, The News daily quoted its sources as saying.
The ISI official "conclusively authenticated" the delivery of the memo before Kayani took up the issue "with all seriousness" with President Zardari and Prime Minister Yousuf Raza Gilani.
It was "only after the ISI's satisfaction over the kind of evidence" that Ijaz produced that Kayani took up the matter, the report said.
Mullen has confirmed that he received the memo but said he took no action on it.
The memo committed Pakistan to revamping its national security set-up in exchange for US assistance to prevent a possible military takeover in the wake of the American raid that killed Osama bin Laden on May 2.
Ijaz has alleged Pakistan's Ambassador to the US Husain Haqqani was the person who asked him to draft the memo.
Haqqani, who has been called to Islamabad to explain his position, has denied that he played any role in fashioning or delivering the memo.
The News reported that Ijaz showed to the ISI all relevant messages, emails and other evidence to prove that Haqqani was the person who initiated and drafted the memo.
Ijaz told Geo News in an interview that he had already shared his evidence with some Pakistani officials.
The report claimed the memo remained a "non-issue" for the President and Prime Minister till Kayani took a clear stance that this was too serious to be overlooked.
Haqqani, an outspoken critic of military dictatorships, has had an uneasy relationship with Pakistan's security establishment since he was appointed the envoy to the US in 2008.
However, he has served as a vital link between Pakistan's weak civilian leadership and the US administration.