* Rebels, govt have met mediators, not each other
* More than 1,000 killed since violence began
* Fighting continued on Friday in vast Jonglei state
By Aaron Maasho
ADDIS ABABA, Jan 4 (Reuters) - Mediators said it was now unclear if South Sudanese rebels would start face-to-face peace talks with the government on Saturday, dampening hopes of a swift end to weeks of ethnic fighting...