You should not have a problem. You can register uk domain names easy so Us should be easy also even if you do not live thier.
Technically speaking though, if you have a "bona fide" presence in the US you can as well, although this seems rather vague: Prospective Registrants will certify compliance with Category 3 Nexus based upon substantial lawful contacts with, or lawful activities in, the United States. Factors that should be considered in determining whether an entity or organization has a bona fide presence in the United States shall include, without limitation, whether such prospective usTLD domain name Registrant: ·Regularly performs lawful activities within the United States related to the purposes for which the entity or organization is constituted (e.g., selling goods or providing services to customers, conducting regular training activities, attending conferences), provided such activities are not conducted solely or primarily to permit it to register for a usTLD domain name and are lawful under the laws and regulations of the United States and satisfy policies for the usTLD, including policies approved and/or mandated by the DoC; ·Maintains an office or other facility in the United States for a lawful business, noncommercial, educational or governmental purpose, and not solely or primarily to permit it to register for a usTLD domain name. So I'm not exactly sure if an affiliate site for example qualifies as "bona fide".
I was about to post the exact same question. Just clarifying. Would i be asked by the domain registrar(eg godaddy) to fill in some undertaking that i am from US or its upto me?(or they will deny the domain based on my profile already entered with them?) What if the site is targeted at a US audience although i am not a US citizen?
Godaddy asks whether you are a US citizen or not then I don't know what happens. Domainsite gives you the other options as well such as whether you have a "bona fide" presence in the US. I've decided to stay away from them for now as the sites I wanted them for are going to be strictly for natural traffic and I don't want any problems in the future and have my SEO work go to waste.