It was not immediately clear if those killed included combatants.
The coalition, which says it takes all precautions to minimize civilian casualties, could not be reached for comment.
The war has killed more than 10,000 people and displaced more than 3 million.
The fighting has caused a humanitarian catastrophe which the UN says is the world's worst, pushing seven million people to the brink of famine and sparking a cholera outbreak that the World Health Organisation says has killed 2,000 people.