The Trump administration on Thursday imposed sanctions on Iraj Masjedi, a general in the Islamic Revolutionary Guard Corps' overseas operations branch and Iran’s ambassador to Iraq.
The US Treasury Department accused Gen Masjedi, a leader in the IRGC's Quds Force, of having direct ties with Iraqi militias.
Washington also imposed sanctions on Hezbollah figures and Iranian bodies.
“Masjedi has overseen a programme of training and support to Iraqi militia groups, and he has directed or supported groups that are responsible for attacks that have killed and wounded US and coalition forces in Iraq,” the department said.
It also accused him of enabling financial transfers on behalf of the IRGC from the time it was under the leadership of Qassem Suleimani, who was killed by a US drone strike in Baghdad in January, until now.
The department said Gen Masjedi organised the transfers with the help of the Quds Force's finance manager Hushang Allahdad, under the directions of Suleimani and his successor, Esmail Ghaani.
It said that most recently, Gen Masjedi provided direct assistance in obtaining tens of billions of dinars on behalf of the Revolutionary Guard in Iraq.
US Secretary of Treasury Steven Mnuchin accused Iran of threatening Iraq’s security.
“The Iranian regime threatens Iraq’s security and sovereignty by appointing IRGC-QF officials as ambassadors in the region to carry out their destabilising foreign agenda,” Mr Mnuchin said.
The US also sanctioned two members of the central council of the Lebanese militant group Hezbollah. They were Nabil Qaouk and Hassan Al Baghdadi.
“The central council is responsible for identifying and electing the group’s highest decision-making body, the Shura Council, which formulates policy and asserts control over all aspects of Hezbollah’s activities, including its military activities,” Mr Mnuchin said.
"We must continue to hold Hezbollah accountable for its horrific actions as we approach the 37th anniversary of Hezbollah bombing of the US Marine barracks in Beirut, Lebanon."
The anniversary is on October 23 and Hezbollah has not claimed responsibility for the bombing but is regarded by the US as the culprit.
Iranian attempts to influence elections punished
The US also placed sanctions on “five Iranian entities for attempting to influence elections in the US".
They are the IRGC, the Quds Force, Bayan Rasaneh Gostar Institute, the Iranian Islamic Radio and Television Union and International Union of Virtual Media.
“This administration is committed to ensuring the integrity of the US election system and will continue to counter efforts from any foreign actor that threatens our electoral processes,” Mr Mnuchin said.