Assuming the diamonds are bought into Liberty from Rheinland, then there's no issue with it from Liberty's perspective. Taking things out of Liberty on the other hand...
Rheinland applies the same policy; so whichever way you do it you're going to be breaking someone's laws. There's a few exceptions to both embargoes, but none that apply to mined materials. The embargo laws (or links to them)are floating around in this thread if you want to take a look.