FILE--- In this file photo of Friday, May 21, 2010 file photo Government of South Sudan Vice President ,Riek Machar, front left, and President Salva Kiir, of South Sudan pay respects at the grave of late southern Sudanese rebel leader Dr. John Garang in Juba. Sporadic gunfire rang out early Monday, Dec. 16, 2013, in the South Sudan capital, Juba, in what a senior military official said were clashes between factions of the country's military. There has been political tension in the world's youngest nation since South Sudan President Kiir sacked Riek Machar as his deputy in July. The local Sudan Tribune newspaper reported on its website that clashes erupted late Sunday between members of the presidential guard in fighting that seemed to pit soldiers from Kiira's Dinka tribe against those from the Nuer tribe of Machar. (AP Photo/Pete Muller-File)