* Juba says detainees could join talks if held in city
* Peace talks in Addis in limbo over detainees' release
* World's newest state on the brink of civil war (Adds detainees back peace talks - IGAD envoys)
By Aaron Maasho and Carl Odera
ADDIS ABABA/JUBA, Jan 8 (Reuters) - South Sudanese rebels rejected a government plan on Wednesday to end a dispute over detainees and unblock peace ...