It is up to you which option you'll take. The Ambassador can give you second choice - to talk to Colonel Hsu at Camp McCarran, who prefers more peaceful approach. If you take this solution, it will probably end with the shooting, so you can ask for another option. You'll be sent to Colonel Moore, who is stationed at the Hoover Dam. If you haven't taken the quest for the King and have decided to return to the Ambassador, you'll receive further instructions.
