NIAMEY (Reuters) -Gunmen killed 69 people including a mayor in an attack in a remote area of southwest Niger, the interior minister said on Thursday, part of a wave of violence against civilians that has swept the country this year. The area is overrun by militants associated with a local affiliate of Islamic State that has killed hundreds of civilians in rural communities this year. Fifteen people survived and a search operation was underway, Interior Minister Alkache Alhada said on state television.