The United States on Tuesday imposed fresh sanctions on a network of companies and individuals in Iran, Turkey and the United Arab Emirates it said was transferring billions of dollars and euros to Iran's elite Revolutionary Guard.
The US Treasury said it was blacklisting 25 people and entities, including front companies based in the three countries, associated with Iran's Islamic Revolutionary Guard Corps (IRGC) and the Ministry of Defence and Armed Forces Logistics (MODAFL).
The targeted institutions include banks and other financial institutions, including Ansar Bank, Atlas Exchange, Iranian Atlas Company.
"We are targeting a vast network of front companies and individuals located in Iran, Turkey, and the UAE to disrupt a scheme the Iranian regime has used to illicitly move more than a billion dollars in funds," Treasury Secretary Steven Mnuchin said in a statement.
The sanctions seek to lock those named out of the global financial system by banning US citizens and US businesses - including international banks with a US presence - from doing business with them.
Mnuchin said the IRGC and MODAFL continued to try to evade sanctions to help Iran's government fund terrorism and destabilise the Middle East.
"Any foreign financial institution that knowingly facilitates a significant transaction for any of the individuals or entities designated today could be subject to US sanctions," the Treasury warned.
The 25 named were mostly relatively small trading and money exchange firms, dubbed by the Treasury "front companies", and their owners and managers who worked with Ansar Bank and Ansar Exchange.
"This vast network is just the latest example of the Iranian regime's use of deceptive practices to exploit the global financial system and divert resources to sanctioned entities," said Treasury Under Secretary for Terrorism and Financial Intelligence Sigal Mandelker.
The US reimposed sanctions against Iran after US President Donald Trump withdrew from a 2015 nuclear deal between Tehran and six world powers, and moved to isolate Tehran. According to Trump, Tehran was "not living up to the spirit of the deal".
In January, however, CIA Director Gina Haspel told Congress that Iran continued to comply with the terms of the deal.
The US has also imposed a string of new sanctions, including against the IRGC and its external arm, Quds Force, to choke off funding for its overseas operations.
The IRGC is by far Iran's most powerful security organisation and has control over large stakes in Iran's economy and a huge influence in its political system.