War-torn South Sudan faces a catastrophic \"tipping point\" amid famine and ge**cide warnings, an aid agency said Thursday, as the conflict entered its fifth month with ** sign of bloodshed ending. \"We either act **w or millions will pay the price,\" Oxfam chief executive Mark Goldring said. President Salva Kiir and rebel chief Riek Machar signed a fresh ceasefire last week but fighting broke out hours later, the second time in the five-month conflict that a truce has failed to stick.