I feel that with the UN it's not so much that countries avoid accountability, while they do, it's also that the UN lacks any real authority and means to enforce the rules/regulations that are agreed upon concerning Human Rights. Or anything else for that matter. The UN does not have the same resources as countries like France, Britain, and the United States, it doesn't have an army per se, and their peacekeeping missions are often a failure because of it. Without proper enforcement mechanisms, no international organization will be as useful as if we need it to be.

Then begs the question of how do IO's effectively enforce their regulations on sovereign nations? That's hard to tell. Take the NPT for example. One of the provisions of the treaty is that the IAEA ( International Atomic Energy ) is to inspect every signatory's nuclear facility, and when they are found to be in violation of the IAEA's standards, the UN is supposed to issue sanctions. The treaty also calls for a path for disarmament, but without any real enforcement mechanism, the UN can't do either of those things.