Pakistan's ambassador to the US, Hussain Haqqani, has flown into Islamabad after being summoned to answer allegations that he wrote a memo that asked for US help against the Pakistani army on behalf of President Asif Ali Zardari.
Haqqani, who has offered to resign despite denying the allegations, is expected to meet Zardari and other senior officials.
Haqqani, a close aide of Zardari, has played an important role in helping Pakistan's civilian government navigate turbulent relations with the US, which deteriorated after the raid that killed Osama bin Laden in Pakistan in May.
Local media reports in Pakistan on Thursday implicated Haqqani in a memo allegedly sent from Zardari to Admiral Mike Mullen, then the top military officer in the US, that sought to curtail Pakistan's military after it was humiliated by the bin Laden killing.
Zardari reportedly feared that the military might seize power as one way to limit the hugely damaging fallout in Pakistan after US special forces killed bin Laden in the garrison city of Abbottabad on May 2.
In remarks to CNN on Wednesday, Haqqani denied writing the memo but confirmed he had offered to resign if it would end "the vilification against the democratic government of Pakistan".
"No memo of the kind being discussed in the media was drafted or delivered by me," Haqqani said. "I have not been named so far as having done anything wrong by anyone except through innuendo."
Haqqani said he was being targeted by part of ongoing "smear campaigns".
Rehman Malik, the Pakistani interior minister, has accused the media of hounding Zardari over the memo, the existence of which was revealed in an op-ed last month by Mansoor Ijaz, a US businessman.
Malik has said that Haqqani will explain his role.
Ijaz told the Rueters news agency that Haqqani called him on May 9, one week after bin Laden was killed to help get a message to US officials.
"The memo's content in its entirety originated from him," Ijaz said, referring to Haqqani.
"At a certain point he started talking so fast, I opened up my computer and I started typing the basic outline of the verbal message he wanted me to transmit."
"He was originally asking me to deliver a verbal message. And when I went back to my US interlocutors - all three of them - said they wouldn't touch this unless it was in writing."
Ijaz said a memo was delivered to Mullen on May 10 and that it suggested a "new national security team" in Pakistan would end troublesome relations between Pakistani intelligence and Afghan fighters, namely the Taliban and its Haqqani faction.