Heavy gunfire and artillery shelling by Afghan border forces killed six civilians across the border in Pakistan on Sunday and wounded another 17, the Pakistan army said. Pakistani troops retaliated at the Chaman border crossing in southwestern Balochistan province, the army said in a statement, without giving details of any losses on the other side. Afghan official Noor Ahmad, in Kandahar, the province on the Afghan side of the border, told Reuters the incident was accidental and the situation had returned to normal after the two sides had a meeting. He gave no further details on any casualtie…