US President Barack Obama has signed an executive order authorising sanctions against anyone aggravating the conflict in South Sudan.
The order sets out a list of offences for which sanctions may be imposed, including attacking UN peacekeepers and commissioning human rights abuses.
In December, fighting broke out between troops loyal to President Salvar Kiir and his sacked deputy, Riek Machar.
The South Sudanese government says it is considering its response.
South Sudanese Presidential spokesman Ateny Wek Ateng told the BBC that ministers were now studying the US order.
The conflict has forced more than 860,000 people to flee their homes.
A ceasefire was agreed between the two sides towards the end of January, but they have accused each other of violating it.
Peace talks between the two sides are being hosted in neighbouring Ethiopia.
The executive order authorises sanctions against both individuals and entities who take part in a wide number of offences, including: threatening "the peace, security, or stability of South Sudan", obstructing the peace talks and the use or recruitment of child soldiers.
Many people have fled to Kenya, Sudan or Uganda, while those in South Sudan are sheltering in UN bases
"The United States will not stand by as those entrusted with South Sudan's future put their own interests above those of their people," White House spokesman Jay Carney said, according to AFP.
"Both the government of South Sudan and Riek Machar's rebels must immediately engage in and follow through on the inclusive peace process... and resolve this conflict.
"The people of South Sudan are calling for peace. There is no room for excuses or delay."
Reports say the EU and UN Security Council are also considering similar actions.
Despite the 23 January ceasefire deal, sporadic fighting has continued.
South Sudan, the world's newest nation, became independent after seceding from Sudan in 2011.
Fighting erupted in the South Sudan capital, Juba, in mid-December. It followed a political power struggle between President Salva Kiir and his ex-deputy Riek Machar. The squabble has taken on an ethnic dimension as politicians' political bases are often ethnic.
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.
Both Sudan and the South are reliant on oil revenue, which accounts for 98% of South Sudan's budget. They have fiercely disagreed over how to divide the oil wealth of the former united state - at one time production was shutdown for more than a year. Some 75% of the oil lies in the South but all the pipelines run north.
The two Sudans are very different geographically. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.
After gaining independence in 2011, South Sudan is the world's newest country - and one of its poorest. Figures from 2010 show some 69% of households now have access to clean water - up from 48% in 2006. However, just 2% of households have water on the premises.
Just 29% of children attend primary school in South Sudan - however, this is also an improvement on the 16% recorded in 2006. About 32% of primary-age boys attend, while just 25% of girls do. Overall, 64% of children who begin primary school reach the last grade.
Almost 28% of children under the age of five in South Sudan are moderately or severely underweight. This compares with the 33% recorded in 2006. Unity state has the highest proportion of children suffering malnourishment (46%), while Central Equatoria has the lowest (17%).
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