The UN Security Council on Friday rejected a US-drafted resolution on imposing an arms embargo and sanctions on South Sudan amid divisions over how to pressure leaders to end the three-year war.
The measure presented by the United States garnered only seven votes in favour in the 15-member council, while eight countries including Russia, China and Japan abstained.
Nine votes and no veto are required for resolutions to be adopted in the council.
The United States, backed by Britain and France, had argued that cutting off the arms flow was urgently needed following UN warnings of a risk of mass atrocities.
But Russia, China, Japan, Malaysia, Venezuela and more importantly, the three African council members — Angola, Egypt and Senegal — were not swayed and they all abstained.
"This should not have been a contentious resolution," US Ambassador Samantha Power told the council after the vote.
"History is going to be a very harsh judge of their decision," said Ms Power, arguing that those who declined to support the measure offered no alternative course to try to end the bloodshed.
The outcome was a setback for the United States, which helped South Sudan gain independence in 2011 but has been unable to steer the country away from a war that erupted two years later.
The United States had also sought to put rebel leader Dr Reik Machar, army chief Paul Malong and Information Minister Michael Makuei on a sanctions blacklist, subjecting them to an assets freeze and a global travel ban.
Japan, which has some 350 troops serving in the UN mission in South Sudan, had warned that the measure would have antagonized President Salva Kiir's government and put peacekeepers' lives at risk.
Opponents of the sanctions pointed to President Kiir's call for a national dialogue to restore peace, saying that initiative must be given a chance.
"Japan believes that it would be counter-productive to introduce additional sanction measures at a time when the transitional government is making some positive moves," said Japanese Ambassador Koro Bessho.
In veiled criticism of the United States, French Ambassador Francois Delattre said the draft resolution should have been put to a vote earlier, when more council members were on board.
The world's youngest nation, South Sudan descended into war in December 2013, leaving tens of thousands dead and more than 3.1 million people displaced.
Six non-governmental organizations expressed disappointment and warned it could embolden the warring sides on the ground.
"The Security Council had an opportunity to show that it stands with the civilian victims of this conflict," said Akshaya Kumar, from Human Rights Watch.
"Instead, this failure gives the warring parties in South Sudan a green light to buy more weapons and materiel that will end up being used against civilians."
There is growing alarm over the humanitarian crisis in the country as the conflict enters its fourth year.
More than six million people — half of South Sudan's population — are in need of urgent aid and humanitarian organizations expect this number to rise by 20 to 30 per cent next year.
Some 1.3 million South Sudanese have fled across borders as refugees, including 383,000 who have fled to Uganda since July, according to UN figures.