The US has warned that military atrocities in South Sudan and the stalling of the peace process will not go unpunished.

The US envoy to the United Nations, Ms Niki Haley, issued the warning on Tuesday while briefing the Security Council at the New York headquarters.

She said her country had run out of patience, listening to excuses from the South Sudan leaders, adding they had the last chance to salvage the 2015 peace agreement and restore peace and stability.

Ms Haley told the Security Council that the people of South Sudan were suffering and the promise of their hard-fought US-supported independence was slipping away.

The US recently sanctioned three South Sudan leaders for war and corruption-related crimes.

"The warring parties must commit themselves to the revitalisation process put forward by the Inter-Governmental Authority on Development (Igad) to resuscitate the peace agreement and to do quickly for time is running short," she noted.

READ: Trump administration sanctions 3 officials for South Sudan conflict

South Sudanese President Salva Kiir over the weekend vowed to end the war in the country.

He also admitted that he was well informed about the suffering the people of the young nation were facing.

"I can't get up in the morning and all the children are crying, let us turn a new page for peace and stability in the country," President Kiir said.

South Sudan got independence from neighbouring Sudan in 2011. But the young nation quickly plunged into a civil war in 2013 after President Kiir accused his former deputy, Dr Riek Machar, of attempting a coup.

The war has claimed tens of thousands of lives and displaced millions of others, according to the UN.

So far, 7.6 million people in South Sudan were in desperate need of humanitarian aid.