NEW : U.N. leader says South Sudan violence shows `` some signs '' of spreading . NEW : U.N. reports 500 killed in U.S. , U.N. says . NEW : South Sudan Red Cross 's Marie-Louise Gumuchian urges president to end the violence that has killed 500 . Numerous armed groups remain active in the oil-rich country . NEW : South Sudan government must resume dialogue with opposition , Ban adds .
NEW : U.N. leader says South Sudan violence shows `` some signs '' of spreading . NEW : U.N. reports 500 killed in U.S. , U.N. says . NEW : South Sudan Red Cross 's Marie-Louise Gumuchian urges president to end the violence that has killed 500 . NEW : South Sudan government must resume dialogue with opposition , Ban adds .