How can I contact the USA Embassy or to get other diplomatic listings?

The U.S. Embassy is in Belize City. The Ambassador’s phone is # 02-77161 (from the U.S. dial 011-501-2-77161.). The British High Commission is located in Belmopan on Embassy Square # 08-22146/22717. Canada, the U.K., Mexico, Guatemala, Costa Rica, Taiwan and about a dozen other countries have ambassadors or other representatives either in Belize City or Belmopan.

This web-based tool finds the nearest US embassies and consulates to any
location in the world:
http://www.aneki.com/nearest_embassy_consulate.php