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 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.
“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.