Zanzibar's President will stay in office until fresh elections can be held on the semi-autonomous Tanzanian Islands, according to a local government statement.
The region's election commission annulled a recent vote citing "gross violations".
The main opposition group Civic United Front (CUF) had originally claimed victory ahead of the result, but have since called on supporters to remain calm during this latest period of uncertainty in Zanzibar's history.
FSN's Dan Ashby reports from the Tanzanian City Dar es Salaam
IN: I spoke to...'
OUT: SOC
DUR: 33 secs