The US Treasury’s Office of Foreign Assets Control (OFAC) has targeted six individuals and three entities that it claims are part of an Iranian-Russian network providing millions of barrels of oil to the government of Syrian President Bashar al-Assad.

In a statement put out on November 20, OFAC also alleged proceeds generated by the network fund the militant groups Hamas and Hezbollah.

US officials said Russia facilitated the delivery of Iranian oil to Syria using a range of mechanisms in trying to conceal shipments and payments.

"Today we are acting against a complex scheme Iran and Russia have used to bolster the Assad regime and generate funds for Iranian malign activity," Treasury Secretary Steven Mnuchin said in a statement.

Leonid Slutsky, chairman of the Foreign Affairs Committee in the lower house of Russia's parliament, the State Duma, described the US sanctions as "absolutely illegal and unlawful".

Russia and Iran have provided Assad with essential support throughout the Syrian Civil War, which began in March 2011 and has claimed the lives of more than 400,000 people.

The list of sanctioned entities and persons released by OFAC includes Syrian national Mohammad Amer Alchwiki and his Russia-based company, Global Vision Group, Russia's state-owned company Promsyrioimport, and its deputy director, Andrei Dogayev, who is a Russian citizen.

Other targets are Iran's Tadbir Kish Medical and Pharmaceutical Company, Iranian nationals Rasoul Sajjad and Hossein Yaghoubi Miab, Syrian national Hajji Abd al-Nasir, and Lebanese national Muhammad Qasim al-Bazzal.

The sanctions block any of their assets under US jurisdiction and warn non-US institutions against conducting transactions with them. Any institution that ignores the warning runs the risk of secondary sanctions.