The U.S. on Wednesday admitted that its helicopters had made a mistake last Wednesday when they shot and killed two Frontier Corps personnel and injured four others, triggering the week-long stand-off between Pakistan and the North Atlantic Treaty Organisation (NATO). Describing the aerial strike as a “terrible accident”, U.S. Ambassador in Pakistan, Anne W. Patterson, apologised for the accident late Wednesday evening after a joint investigation established that the American helicopters had mistaken FC personnel to be insurgents they had been pursuing. “We extend our deepest apology to Pakistan and the families of the Frontier Scouts who were killed and injured,” the Ambassador said in a statement. Maintaining that Pakistan’s “brave security forces” are America’s allies in a war that threatens both countries, she added that the U.S. will coordinate with the government of Pakistan to prevent such tragic accidents from taking place in the future. Ever since the aerial strike, Pakistan has closed its Torkham border post to NATO vehicles ferrying goods and oil to the International Security Assistance Force in Afghanistan. Also, the past week has seen regular attacks on NATO containers in different parts of the country.