If you are in Brunei then you can find the US Embassy located in Bandar Seri Begawan not far from the Malaysian High Commission in the country. If you have any questions about assistance from the Embassy then it is best to call or to email them. You can ask about the US Visa or other assistance as an American citizen from the Embassy. Note the map and telephone and email address for the Embassy in Brunei.
US Embassy in Brunei