(Anjum Naveed — Associated Press)

“We are increasingly troubled by Ambassador Haqqani’s treatment since he returned home to Pakistan, including the travel ban imposed on him,” said a statement by Republican Sens. John McCain (Ariz.) and Mark Kirk (Ill.), and Sen. Joseph Lieberman (I-Conn.). They urged Pakistani authorities “to resolve this matter swiftly,” consistent with the rule of law, and to prevent the investigation of Haqqani “from becoming a political tool for revenge against an honorable man.”

“This matter” refers to allegations by a U.S.-Pakistani entrepreneur that Haqqani enlisted him, in the wake of the U.S. raid that killed Osama bin Laden last spring, to solicit American help in preventing a supposedly pending military takeover. The entrepreneur, Mansoor Ijaz, sent a memo to retired Adm. Mike Mullen, then chairman of the Joint Chiefs of Staff, which he subsequently said was approved by Haqqani and Pakistani President Asif Ali Zardari.

Both Zardari and Haqqani have denied any authorship or approval of the memo and described Ijaz as a publicity-seeker. Mullen said he ignored the document because it had no signature and made little sense; Pentagon aides have said its description of a threatened coup did not comport with their own intelligence on what was going on inside Pakistan at the time.

But the issue quickly became the latest stage on which always-simmering military-civilian tensions in Pakistani are playing out. Haqqani was ordered home, forced to resign and banned from leaving the country during a Supreme Court investigation amid allegations of treason and heated media commentary. The former ambassador’s legal team has challenged the court’s authority in the matter.

In an interview this week with Britain’s Daily Telegraph, Haqqani said the allegations against him were part of a “psychological war” against Zardari’s government by “certain powerful quarters.”

He said he feared for his life, and had taken refuge in the home of Pakistani Prime Minister Yusuf Reza Gilani. “There are clear security concerns, given the hysteria generated against me,” Haqqani told the Telegraph. Haqqani noted that a close friend, Punjab governor Salman Taseer, was assassinated last year by one of his own security guards after he spoke up against Pakistan’s harsh anti-blasphemy laws.

“I’m being called a traitor and an American lackey in the media with the clear encouragement of certain powerful quarters even though I’ve not been charged legally with anything,” Haqqani said.

The case has put the United States, which hopes to calm U.S.-Pakistan relations after a series of upheavals last year, in a difficult situation. While privately concerned about Haqqani, U.S. officials have limited their public statements to calls for due legal process.

“Husain Haqqani served Pakistan honorably as its ambassador to the United States,” the senators’ statement said. “While we did not always agree...and our exchange of views could be spirited at times, we always had the highest respect for him and knew he was serving his nation and government with patriotism and distinction..”

“Like many in Washington, we are closely following Ambassador Haqqani’s case,” they said. “We look forward to the day when he can once again serve the government and people of Pakistan as one of the nation’s finest leaders.”