ISLAMABAD: Militants crossed into Pakistan from Afghanistan and killed 13 Pakistani troops, beheading seven of them, the Pakistani military charged, and the country’s outraged new prime minister said he would protest to the Afghan president. The border skirmish is a new sign of tensions between the uneasy neighbors. Pakistan has complained that militants use parts of Afghanistan for sanctuary to stage attacks inside Pakistan. That claim helps Islamabad counter frequent US and NATO complaints that militants behind much of the violence in Afghanistan come from Pakistan. Pakistani military officials said militants from Afghanistan crossed in the northwestern Pakistan’s Upper Dir region Sunday night and clashed with Pakistan forces on a patrol.