Pakistan stopped oil tankers and trucks carrying NATO supplies to Afghanistan Thursday, apparently in retaliation after NATO helicopters attacked a security post near the countries’ border, killing three paramilitary soldiers and injuring three more. It’s unknown whether the Torkham border crossing, north of Peshawar, will be reopened. Western troops get most of their nonlethal equipment through the crossing, and such a closure is not only rare but a sign of a deteriorating relationship between Pakistan and the U.S. The helicopters had fired on posts in Mandati Kandaw and nearby Karachi; both places border Afghanistan’s Paktia province. Last weekend, three American air strikes killed more than 50 people thought to be part of the militant Haqqani network in Pakistan. American military officials tried to soothe Pakistan by saying those attacks were in self-defense.