(BBC) – The helicopters arrived shortly after midday and sent a rocket hurtling into an area at the back of the crowd where children were sitting. As people began to flee, witnesses said, heavy machine gun fire followed them. It was the latest deadly example of how a ferocious new air campaign against the Taliban has caused a spike in civilian casualties from US and Afghan air operations. This Afghan Air Force attack on 2 April in north-eastern Kunduz province killed at least 36 people and injured 71, the UN says. Although witnesses said Taliban fighters and senior figures were in the crowd, 30 of those killed were children.