ISLAMABAD: You know a friendship has gone sour when you start making mean jokes about your friend in front of his most bitter nemesis.  

So it was a bad sign this week when the US defense secretary joshed in front of an audience of Indians about how Washington kept Pakistan in the dark about the raid that killed al-Qaida leader Osama bin Laden a year ago.

''They didn't know about our operation. That was the whole idea,'' Leon Panetta said with a chuckle at a Q&A session after a speech in New Delhi, raising laughs from the audience.

The Bin Laden raid by US commandos in a Pakistani town infuriated Islamabad because it had no advance notice, and it was seen by Pakistan's powerful military as a humiliation.

The US and Pakistan are starting to look more like enemies than allies, threatening the US fight against Taliban and al-Qaida militants based in the country and efforts to stabilize neighboring Afghanistan before American troops withdraw.

Long plagued by frustration and mistrust, the relationship has plunged to its lowest level since the 9/11 attacks forced the countries into a tight but awkward embrace over a decade ago. The US has lost its patience with Pakistan and taken the gloves off to make its anger clear.

''It has taken on attributes and characteristics now of a near adversarial relationship, even though neither side wants it to be that way,'' said Maleeha Lodhi, who was serving as Pakistan's ambassador to the US at the time of the Sept. 11, 2001 terror attacks and was key in hurriedly putting together the two countries' alliance.

The latest irritant is Pakistan's refusal to end its six-month blockade of Nato troop supplies meant for Afghanistan. Even if that issue is resolved, however, the relationship may be on an irreversible downward slide.

The main source of US anger is Pakistan's unwillingness to go after militants using its territory to launch attacks against American troops in Afghanistan.

On the Pakistani side, officials are fed up with Washington's constant demands for more without addressing Islamabad's concerns or sufficiently appreciating the country's sacrifice. Pakistan has lost thousands of troops fighting a domestic Taliban insurgency fueled partly by resentment of the alliance with the US

Panetta's comments about the bin Laden raid may have been unscripted, but others he made while in India and Afghanistan seemed calculated to step up pressure on Pakistan.

He stressed Washington's strong relationship with India, which Islamabad considers its main, historic enemy, and defended unpopular American drone attacks in Pakistan.

He also said in unusually sharp terms that the US was running out of patience with Islamabad's failure to go after the Pakistan-based Haqqani network, considered the most dangerous militant group fighting in Afghanistan.

Many analysts believe Pakistan is reluctant to target the Haqqanis and other Afghan militants based on its soil because they could be useful allies in Afghanistan after foreign forces withdraw, especially in countering the influence of India.

A senior US official described the relationship as ''the worst it has ever been.''

''This is from Washington's point of view and from Pakistan's point of view, and even among the real well-wishers on both sides who are appalled and befuddled that we can't get past all of this and move beyond,'' said the official, speaking on condition of anonymity because of the sensitivity of the issue.

After years of frosty relations caused by Pakistan's nuclear weapons program, Washington and Islamabad were thrust together on Sept. 11, 2001, when al-Qaida attacked New York and Washington.

The US demanded Pakistan support the war against bin Laden and his Taliban hosts in Afghanistan. The US directed billions of dollars in aid to Pakistan and sought to convince Islamabad it was not simply interested in a ''transactional'' relationship based on counterterrorism cooperation, but wanted a long-term strategic partnership.

US officials have largely abandoned that argument over the past 18 months as the relationship has suffered repeated crises.

''Because of the toxic atmosphere on both sides, the two countries cannot even work in a transactional way,'' said Lodhi, the former Pakistani ambassador.

In January 2011, a CIA contractor sparked outrage when he shot to death two Pakistanis in the city of Lahore who he claimed were trying to rob him. Anger over the incident was still simmering when the US killed bin Laden in May.