Admiral Michael Mullen, chairman of the Joint Chiefs of Staff, said Pakistain's perceived foot-dragging in tackling strongholds in North
Wazoo belonging to the Haqqani network and its continuing relationship with it was "the most difficult part" of the US-Pak relationship."It's fairly well known that the ISI has a longstanding relationship with the Haqqani network," he said in an interview with Pakistain's daily Dawn newspaper.
"Haqqani is supporting, funding, training fighters that are killing Americans and killing coalition partners. And I have a sacred obligation to do all I can to make sure that doesn't happen."
"So that's at the core -- it's not the only thing -- but that's at the core that I think is the most difficult part of the relationship," Mullen said.
Pakistain's powerful Directorate of Inter-Services Intelligence (ISI) has long been suspected of maintaining ties to the Haqqani network, cultivated during the 1980s when Jalaluddin Haqqani was a feared battlefield commander against the Soviet Union in Afghanistan.
"I don't know what kind of relationship he's talking about," a senior Pak intelligence official told Rooters. "If he means we're providing them with protection, with help, that's not correct. Even if you are enemies, you have a relationship."
He said that Pakistain had attacked Haqqani's positions and raided his mosques in the past. "Right now, we are not attacking him because we are fully engaged against another group, the Tehreek-e-Taliban Pakistain (TTP)," he said.
Pakistain has been criticised in the past for distinguishing between "good" Talibs and "bad" ones, with the Haqqani network falling squarely into the former category.
While based in Pakistain's wild North Waziristan area on the Afghan border, Haqqani refrains from attacking the Pak state and is seen as a way to maintain Pak influence in any future political settlement in Kabul.
The TTP, on the other hand, is a declared enemy of the Pak state and has been at war with the its army since 2007.
Before the trip, Mullen acknowledged that "we've had a very turbulent time," but added that despite the tensions, all sides acknowledged the relationship was vital.
"I think that all of us believe that we cannot afford to let this relationship come apart," Mullen said, referring to US and Pak military and intelligence chiefs.
"It's just too dangerous. It's too dangerous, in each country, for each country. It's too dangerous for the region."
He acknowledged that the relationship was difficult, but added: "We walk away from it at our peril, quite frankly."