The commander of US and NATO forces in Afghanistan, General David Petraeus, issued new guidelines to troops on Wednesday, emphasizing the need to avoid civilian casualties, NATO said. "The directive firmly places the presence of civilians at the centre of every decision involving the use of force" and ensures "that some areas that may have led to misperceptions are clarified," a statement said. Petraeus took over command of more than 140,000 US and NATO troops in Afghanistan on July 4 from sacked US General Stanley McChrystal.