* 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) - Gunfire rang out again in South Sudan's capital Juba late on Monday hours after President Salva Kiir said his forces had quelled an "attempted coup" by supporters of his sacked deputy.