One of two major border crossings between Pakistan and Afghanistan was closed on Tuesday after a deadly fire exchange between troops from both sides, officials in Islamabad and Kabul said. At least three Afghan civilians including children were killed when Pakistani troops fired at their homes near the Torkham border crossing, Mufti Abdul Mateen, a spokesman for the Afghan interior ministry said. At least seven civilians were wounded on the Pakistani side when the Taliban fighters fired with heavy weapons and artillery, local border official Shaiq Ali told dpa. Hundreds of Pakistani families f…