unite nations unite state threaten tuesday take action south sudan government end violence allow unite nations peacekeepers job u.n. sanction unlikely russia warn move month u.s. ambassador unite nations nikki haley visit south sudan meet president salva kiir capital juba tell u.n. security council word long sufficient unite state prepare pursue additional measure government party matter act end violence ease suffer south sudan say haley senior member president donald trump administration visit south sudan trump administration impose sanction september two senior south sudanese officials former army chief role civil war attack civilians however u.s. push u.n. security council take action south sudan likely resist veto power russia council sanction several senior south sudanese officials side conflict 2015 u.s. bid impose arm embargo december 2016 fail counterproductive impose target sanction counterproductive impose arm embargo measure help break deadlock exacerbate crisis russia deputy u.n. ambassador petr iliichev south sudan spiral civil war late 2013 two years gain independence sudan third 12 million population flee home conflict spark feud kiir dinka former deputy riek machar nuer hold south africa fragile peace deal south sudan break last year east african bloc igad try revive view unjust ongoing attempt place blame persistent unabated violence juba alone do role opposition must reciprocate iliichev say u.n. sanction monitor report early month despite catastrophic condition across south sudan arm force group militias particularly affiliate kiir vice president taban deng gai continue actively impede humanitarian peacekeeping operations u.s. threaten south sudan action russia warn u.n. measure