Pakistan's ambassador to the United States has arrived in Islamabad in the wake of alleged links to a secret offer to Washington by Pakistani President Asif Ali Zardari.

CNN-Pakistan's ambassador to the United States has arrived in Islamabad in the wake of alleged links to a secret offer to Washington by Pakistani President Asif Ali Zardari to cut down the powers of the country's military leadership, two sources within the government in Islamabad told CNN.

Ambassador Husain Haqqani has offered his resignation over the scandal, though the president hasn't yet accepted it.

"I have communicated my willingness to resign or participate in any inquiry that brings an end to the vilification against the democratic government of Pakistan currently being undertaken by some elements in the country," he told CNN last week.

Haqqani's resignation offer follows swirling media reports that Zardari asked Washington in May to help him hold on to power because he feared a military coup after the U.S. raid on Osama bin Laden's compound in Abbottabad, Pakistan.

Last month Pakistani businessman Mansoor Ijaz sparked the political firestorm when he claimed in an op-ed piece for the UK-based Financial Times that a Pakistani diplomat used him to make Zardari's back-channel plea for help by delivering a secret memo to U.S. Admiral Mike Mullen, then Washington's top military official.

Ijaz claimed Zardari offered a new "national security team" to take over the powers of the military leadership in exchange for Washington's assistance.

Media reports in Pakistan have speculated that Haqqani played a key role in the alleged offer.

Haqqani has denied the allegations, saying they are part of ongoing "smear campaigns" that have accused him of trying to undermine Pakistan's armed forces.

"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."

The political controversy threatens to shake an already tense relationship between Pakistan's military and civilian leadership and sets the stage for a potential test of strength between the president and Pakistan's Army Chief Ashfaq Kayani, who is widely believed to be the most powerful man in Pakistan.

Amid growing pressure, Zardari summoned Haqqani to Islamabad.