U.N. Secretary-General Ban Ki-moon is warning that South Sudan will be heading toward genocide unless immediate action is taken to impose an arms embargo and pressure leaders of the world's newest nation to end hate speech, incitement and violence.

The U.N. chief says instability in South Sudan is threatening the region and he urged the Security Council on Monday to impose an arms embargo, which he says would "diminish the capacity of all sides to wage war."

Ban warns that "if we fail to act, South Sudan will be on a trajectory towards mass atrocities."

South Sudan plunged into ethnic violence in 2013 when forces loyal to President Salva Kiir, a Dinka, started battling those loyal to Riek Machar, his former vice president, who is a Nuer.