Part of the problem that gets in the way of any United Nations role is what happened with Libya. The Russians and Chinese went along with a restrained Security Council resolutiion about preventing civilian casualties, and then it was used as a cover for military involvement to escalate the war and bring regime change. (Essentially the same thing that had happened in the case of Iraq.)

Even if the outcome in Libya was a good one - and that word "if" is the crucial one, the regime that operates in Libya is decidedly dodgy, and some consequences in other places, such as Mali have been disastrous - the results in the Security Council have not been at all good. They mean that virtually any restraining resolution is out of the question, because of fear that it will be used in the same way.