United States officials under then-President Barack Obama and current President Donald Trump have argued that a United Nations led arms embargo could stem the flow of weapons into South Sudan.
It is a largely symbolic move, as the U.S. does not export arms to South Sudan.
South Sudan's opposition is threatening to resort to "guerrilla warfare" if peace talks in Ethiopia fail in the coming days as government forces advance on remaining rebel strongholds in the fifth year of civil war.
"We will appeal for a lot of money [.] for right now 2.4 million refugees in neighboring countries including Kenya, a number that we project will rise above 3 million by the end of the year if the conflict does not stop".
Companies and entities seeking a license to export defense materials to South Sudan will be denied under the new restrictions. "Stopping the suffering and violence that have wracked South Sudan and have injured and killed so many people there".
Also, in an unusual shift, the African Union on Monday said it was open to imposing sanctions on leaders violating ceasefires in South Sudan, joining a growing chorus of officials who say those prolonging the conflict must be punished. "We will continue to take actions against those who foment violence and obstruct the peace process", Nauert said.
"Just last month President Kiir promoted three generals who this councel sanctioned in 2015", explained Haley. Humanitarian partners in South Sudan need US$1.7 billion to provide life-saving humanitarian assistance to six million people across the country. "We can not stand by idly as innocent civilians are murdered and raped".
South Sudan gained independence in 2011 but fell into a civil war in 2013, with tens of thousands killed and almost 4 million displaced since.
The conflict has claimed tens of thousands of lives since then, slashed oil production and driven about a third of the population of 12 million from their homes.
South Sudan is the world's youngest country, having gained independence in 2011.
Nauert urged South Sudan's neighbors and other countries to take similar measures.
Last year, the United Nations experts said: "Weapons continue to flow into South Sudan from diverse sources, often with the coordination of neighboring countries".