washington african countries pile pressure south sudan political leaders seem incapable resolve country four-year civil war top u.s. diplomat say wednesday think african colleagues point especially term focus leadership point view behave way irresponsible tom shannon u.s. under-secretary political affairs state department tell reporters shannon speak sideline u.s-african partnerships event u.s. institute peace say washington grow intolerant south sudan leaders challenge work african countries interest see end conflict manmade conflict horrific dimension political leaders measure force cost populations say shannon remark come new usaid administrator mark green travel juba sept. meet south sudan president salva kiir deliver message washington unite state review relationship government trump administration last week impose sanction two senior south sudanese officials former army chief role conflict atrocities civilians attack international missions south sudan south sudan become world new nation gain independence sudan 2011. war break late 2013 quarter population 12 million flee home confidential report unite nations last week say compete efforts end south sudan civil war allow kiir government exploit divisions among international broke east african leaders say june want war side recommit peace deal abandon year ago. among international body try end conflict regional block igad u.n. security council troika south sudan main western backers prior independence african union panel region must pressure south sudan leaders end conflict u.s. diplomat