* President blames supporters of sacked deputy
* Thousands take shelter at U.N. bases in capital
* South Sudan has struggled since 2011 independence
By Carl Odera
JUBA, Dec 16 (Reuters) - South Sudan's President Salva Kiir declared a curfew in the capital Juba on Monday after overnight clashes between rival factions of soldiers that he said were triggered by an "attempted coup"....