The companies and government bodies would in future require special licenses to do business in the United States, the State Department said.
“The South Sudanese Government, and corrupt official actors, use this revenue to purchase weapons and fund irregular militias that undermine the peace, security, and stability of South Sudan,” the department said in a statement.
The groups on the list “are involved in activities that are contrary to the foreign policy interests of the United States,” according to a related Department of Commerce document published on Wednesday.
The South Sudanese government was not immediately available to comment.
Washington has already placed sanctions on South Sudanese military and political figures, and in January imposed an arms embargo to halt the flow of weapons into the country, signaling that it had lost patience with South Sudan’s warring factions for ignoring ceasefires.
Last year, the South Sudanese government said it planned to more than double oil production to 290,000 barrels per day (bpd) in fiscal 2017/2018.
It is the most oil-dependent country in the world, with oil accounting for almost all of its exports and around 60 percent of gross domestic product, according to the World Bank.
The Department of Commerce’s so-called Entity List does not freeze assets but requires that US and foreign companies doing business with those on the list first obtain a license.
The Commerce Department placed the South Sudan Ministry of Mining, the South Sudan Ministry of Petroleum, and state oil firm Nile Petroleum and associated companies on its list.
The list includes Dar Petroleum Operating Company, an oil and gas consortium led by China National Petroleum Corp and Malaysia’s state-run oil and gas firm Petronas, the two largest oil firms operating in South Sudan
The restrictions also cover oil distributor Nyakek and Sons; Greater Pioneer Operating; Juba Petrotech Technical Services; Nigeria’s Oranto Petroleum, and Sudd Petroleum Operating.
Since then, the conflict has claimed tens of thousands of lives, slashed oil production and driven about a third of the population of 12 million from their homes.