The United States has imposed economic sanctions on four energy firms that it accuses of helping to move oil exports for the Quds Force of Iran's elite Islamic Revolutionary Guards Corps (IRGC).

The sanctions announced on January 23 come three weeks after U.S. forces killed the commander of the Quds Force, Major General Qasem Soleimani, in a targeted air strike near Baghdad.

"Today, the United States is taking new steps as part of our maximum economic pressure campaign to deny the Iranian regime all sources of revenue to fund its destabilizing activities," Secretary of State Mike Pompeo said in a statement.

The U.S. Treasury said two of the firms sanctioned were based in Hong Kong, one was in Shanghai, and the other in Dubai.

It said they had together transferred "hundreds of millions of dollars' worth" of exports from the National Iranian Oil Company, a move that helped finance the Quds Force, which has been designated as a foreign terrorist organization by the United States.

"Iran's petrochemical and petroleum sectors are a primary source of funding for the Iranian regime's global terrorist activities and enable its persistent use of violence against its own people," Treasury Secretary Steven Mnuchin said in a statement.

Other entities linked to the IRGC have also recently been targeted by U.S. authorities, including metals companies and oil companies accused of supporting the IRGC.

"All entities and individuals in the petrochemical sector should take notice," Pompeo said.

"The United States will not waver in its commitment to sanctions enforcement. As long as the Iranian regime continues to exploit revenue from its petroleum and petrochemical industries to fund destabilizing activities, we will sanction any entity or individual that facilitates such trade."

The four firms sanctioned are Triliance Petrochemical and Sage Energy of Hong Kong, Peakview Industry in Shanghai, and Beneathco DMCC of Dubai.

With reporting by AFP