The Haqqanis, blamed for some of the deadliest attacks in Afghanistan and whose leaders are understood to be based in the Pakistani tribal district, is one of the thorniest issues between Islamabad and Washington."The Americans have been repeatedly told that they will have to seal off the border on the Afghan side whenever an operation is launched in North Waziristan," a senior Pakistani security official told AFP.Without protecting the porous, mountainous border, militants would simply escape into Afghanistan, where Pakistan has no writ, the official explained.He claimed that Americans have "never been encouraging on this point" and accused them of failing to seal the border when operations were planned twice before in North Waziristan.On August 3, The Wall Street Journal reported that Pakistani and US officials were considering joint counter-terrorism campaigns in Afghanistan and Pakistan against the Haqqanis and Taliban fighters who attack Pakistan.The paper said the campaigns would mark an upturn in cooperation after more than a year of rancorous relations and stamp out major threats facing each country.Pakistani officials later denied any agreement with the United States for a joint operation in North Waziristan, and said "routine" actions on each side of the border "should not be mistaken for 'joint operations'".