President Obama on Thursday signed an executive order allowing sanctions against South Sudan as the nation nears full-scale civil war.
"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 press secretary Jay Carney said.
Fighting between government forces and rebels led by former Vice President Riek Machar have left thousands dead and an estimated 1 million people displaced from their homes. A negotiated ceasefire has done little to curb violence.
The executive order enables Obama to freeze any American-held assets of leaders in South Sudan deemed to be obstructing the political process there. American businesses would also be blocked from doing business with those targeted for sanctions.
The United Kingdom and Norway have also threatened sanctions on both the South Sudanese government and rebel fighters.
Earlier Thursday, a top U.S. Agency for International Development (USAID) official warned that millions of people in the country faced starvation with government and rebel forces blocking the delivery of aid.
"The people of South Sudan cannot afford for aid be delayed," USAID assistant administrator Nancy Lindborg said in an interview with the radio program "South Sudan In Focus."
"The rivers have been closed to humanitarian deliveries... all these instances of humanitarian aid workers being harassed, of being stopped at checkpoints, being forced to pay huge bribes — these are actions that the government and the opposition leadership need to take a very strong stance on and make very clear that, for the people's sake, humanitarian assistance needs to reach them," she said.