Cannot move imported comments to trash

Ultimate Facebook has imported lots of comments, but many of them are not tied to any particular post in Wordpress, it seems to just randomly be grabbing comments from my FB wall and inserting them into my blog. To make matters worse, there doesn't seem to be any way to delete these imported comments. I've tried the normal method of moving them to Trash, but for some reason they don't move and stay right where they are. I've tried deleting several times.
Help?