Three US diplomats held near Russian test site where mystery blast killed five

* US embassy says trio had proper paperwork to travel* August explosion causes radiation levels to surgeA Russian navy official works on the Akula nuclear-powered ballistic missile submarine at the Severodvinsk site in July. The August explosion there killed at least five people. Photograph: Sergei Bobylev/TassThree American diplomats were briefly detained in Russia near the military test site where a mysterious explosion released radiation in August, several Russia state news agencies have repo