The Department of the Treasury announced measures against the Iranian Ministry of Petroleum, the National Iranian Oil Company and the National Iranian Tanker Company and several senior executives. The companies and ministry are "front operations" raising funds for Iran's Islamic Revolutionary Guard Corps-Qods Force and Syrian President Bashar al-Assad's regime, the department said.
"The regime in Iran uses the petroleum sector to fund the destabilising activities of the [Revolutionary Guard]," said Steven Mnuchin, treasury secretary, in a statement. "The Iranian regime continues to prioritise its support for terrorist entities and its nuclear program over the needs of the Iranian people."
The Trump administration has complained about sales of 10 million barrels of Iranian crude oil to Assad's government in 2019. The U.S. imposed sanctions in June on five ship captains for transporting 1.5 million barrels of Iranian gasoline and oil to Venezuela.
The department designated multiple front companies, subsidiaries and executives in the updated sanction list connected to sale of gasoline to Syria. Sanctions were also announced for four people involved in the Venezuela gasoline sale to the Nicolas Maduro regime in Venezuela.
The Trump administration is tightening sanctions on Iran in the hopes of bringing stronger limits on the country's nuclear and ballistic missile programs, after Trump withdrew in 2018 from the landmark Obama-era Iranian nuclear accord, saying it was "defective at its core."
Relations between the United States and Iran deteriorated further when U.S. airstrikes killed top Iranian General Qasem Soleimani in January.
The Trump administration is also helping to build a coalition of Iran's adversaries by brokering deals between Iran's strongest enemy, Israel, and the United Arab Emirates, Bahrain and Sudan.
A week ago, Secretary of State Mike Pompeo threatened economic sanctions on any entity that sells weapons to Iran, after a United Nations Security Council 10-year arms embargo expired Oct. 18.
"For the past 10 years, countries have refrained from selling weapons to Iran under various U.N. measures," Pompeo said last week. "Any country that now challenges this prohibition will be very clearly choosing to fuel conflict and tension over promoting peace and security."
Pompeo also announced sanctions against Iran's defence ministry last month.
Iran's president Hassan Rouhani has refused to negotiate on nuclear arms while U.S. sanctions remain in force.