ISLAMIST militants in northeast Nigeria have executed four aid workers and a private security guard, according to a video seen by Reuters. The International Rescue Committee and Action Against Hunger, both aid groups, confirmed the killing of their colleagues and other humanitarian workers in statements condemning the executions. Last month, the militants released a video in which the hostages identified themselves. The execution underscores the increasing risk for aid workers in northeast Nigeria, where a decade-long conflict with Boko Haram and Islamic State's regional ally has fuelled one of the world's worst humanitarian crises. "You that are working for infidel…