The top U.S. military officer accused Pakistan's intelligence agency of maintaining ties to militants in Afghanistan during a trip to Islamabad on Wednesday that was focused on easing diplomatic tensions. Admiral Michael Mullen, chairman of the Joint Chiefs of Staff, said Pakistan's perceived foot-dragging in tackling strongholds in North Waziristan belonging to the Haqqani network and its continuing relationship with it was "the most difficult part" of the U.S.-Pakistani relationship. "It's fairly well known that the ISI has a longstanding relationship with the Haqqani network," he said in an interview with Pakistan'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."