The only way to do this right would have been to send UN troops right away with all the proper equipment. And if any of the sides objected, then say who and why refused access. None of it was done.
Yes, well would be very nice but the small problem here is that UN troops do not exist -the UN does not maintain a readily deploy-able military force. The UN can pass a resolution to deploy international troops under its aegis that member states would contribute for the particular mission. This process takes a considerable amount of time and is therefore not a viable option here.