United Nations, US:
UN Secretary General Ban Ki-moon urged the leaders of South Sudan's two warring factions to resume peace talks, as he marked three years on Tuesday since the founding of the struggling African nation.
In a statement, Ban invoked the thwarted "hopes and expectations" of South Sudan's people, whose lives for more than half a year have been thrown into upheaval by war.
"On the occasion of the third anniversary of South Sudan's independence, the Secretary-General recalls the hopes and expectations of the people of South Sudan when their country was established on 9 July 2011," the UN statement said.
"Those hopes were dashed by the conflict that broke out in December 2013. Thousands of South Sudanese have been killed, and atrocities have been committed against civilians," Ban said.
"The South Sudanese people are bearing the brunt of the failure to stop the fighting. They are living in squalor, their livelihoods have been lost and they are plagued by hunger, disease and insecurity," he added.
"Over 1.3 million people have been driven from their homes," Ban said, adding that the devastated young nation can expect more of the same, "unless... the parties cooperate."
"The Secretary-General... calls on them to live up to the expectations of their people, lay down their arms and return immediately to the negotiation table," Ban said, pledging UN support to the South Sudanese people as the humanitarian crisis in South Sudan worsens.
The war in the world's youngest nation has claimed thousands - possibly tens of thousands - of lives. It erupted after a power struggle between President Salva Kiir and his former deputy Riek Machar spiraled into brutal ethnic conflict, and peace agreements between the two sides have failed to hold.
Aid agencies have warned that without massive funding, famine zones will be declared within weeks.