The United States on Wednesday imposed sanctions on 15 South Sudanese oil operators that it said were important sources of cash for the government, an action aimed at increasing pressure on President Salva Kiir to end the country’s conflict and humanitarian crisis, Reuters reports.

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 South Sudanese government was not immediately available to comment.

The Commerce Department placed the South Sudan Ministry of Mining, the South Sudan Ministry of Petroleum, and state oil firm Nile Petroleum on its list. The list also includes Dar Petroleum Operating Company, an oil consortium led by China National Petroleum Corp and Malaysia’s Petronas. The restrictions also cover Nyakek and Sons; Greater Pioneer Operating; Juba Petrotech Technical Services; Nigeria’s Oranto Petroleum, and Sudd Petroleum Operating.

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