Why was the nambutu embassy used in casino royale?

Nambutu is a fictional country, so my best bet is that it was used so that the directors would not offend any country in particular (as it implies that the country harbours terrorists).

In my opinion, the Embassy scene was used to show that sometimes diplomatic policy can get in the way of a job being done; as Molaka was under protection from the Nambutu government despite his actions during the chase. It also illustrates Bond's transformation from a 'thug' to a calculating agent.