By Phil Stewart and Chris Allbritton
ISLAMABAD (Reuters) - The top U.S. military officer accused Pakistan's intelligence agency of maintaining ties to militants targeting U.S. troops in neighboring Afghanistan, during a trip to Islamabad on Wednesday.
The comments by Admiral Mike Mullen, chairman of the U.S. military's Joint Chiefs of Staff, were not the first by U.S. officials pointing the finger at elements of Pakistan's Directorate of Inter-Services Intelligence (ISI) and their alleged links to the Haqqani network.
But his forceful, and repeated remarks to Pakistani media about those ties, suggest Washington is not about to back away from calls for Pakistan to take a more assertive stand against Haqqani -- even as the United States seeks to mend diplomatic ties with Islamabad.
U.S.-Pakistan ties have been strained this year by the case of a CIA contractor Raymond Davis, who shot dead two Pakistanis in Lahore on January 27, as well as by tensions in Pakistan over U.S. drone strikes that have fanned anti-American sentiment.
"It's fairly well known that the ISI has a longstanding relationship with the Haqqani network," Mullen told Pakistan's daily Dawn newspaper, one of three interviews he held.
"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," said Mullen, ahead of talks with Pakistan's army chief, General Ashfaq Kayani.
Pakistan's powerful 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.
A senior Pakistani intelligence official rejected any suggestion of collusion.
"I don't know what kind of relationship he's talking about. If he means we're providing them with protection, with help, that's not correct," he said. "Even if you are enemies, you have a relationship."
He said Pakistan 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 Pakistan (TTP)," he said.
Pakistan has been criticized in the past for distinguishing between "good" Taliban militants and "bad" ones, with the Haqqani network falling squarely into the former category.
While based in Pakistan's wild North Waziristan area on the Afghan border, Haqqani refrains from attacking the Pakistani state and is seen as a way to maintain Pakistani influence in any future political settlement in Afghanistan.
The TTP, on the other hand, is a declared enemy of the Pakistani state and has been at war with its army since 2007.
Mullen acknowledged the U.S.-Pakistan relationship had endured a turbulent period because of the Davis case.
A Pakistani court acquitted Davis of murder charges last month after a deal that involved the payment of compensation, or "blood money," to the families of the two men he killed.
Davis said the men were trying to rob him.
"The ability to sustain a very difficult period as we have recently, between Pakistan and the United States, is in some ways indicative of the strength of the relationship," Mullen said.
"That doesn't mean we don't have challenges to continue to address, because we do."
In the wake of the incident, some Pakistani officials have called for sharp cuts in drone attacks. But a U.S. official in Islamabad said the drone programme would continue.
Pakistani journalists pressed Mullen about the drone attacks, with one television reporter asking him to explain to viewers "why drones are still important and why the U.S. is not the proverbial 'bad guy'."
U.S. officials do not publicly acknowledge the U.S. drone programme, leaving Mullen to only restate his confidence in U.S.-Pakistan ties.
"What's really important is the relationship between our two countries," Mullen said.
(Editing by Sophie Hares)