Can the UN be held accountable for the failure to protect civilians?

It seems to me that the root of the failure in South Sudan is that only a much larger mission could have protected more than a small fraction of the civilians there. Basically, peacekeeping missions depend on the prestige of the name, "United Nations Peacekeeping Mission", which depends over the long term on the willingness of the Great Powers to use their might against those who disrespect those missions. The Great Powers had better do their job.