These companies are Aluminat, Pars Amayesh Sanaat Kish, Pishro Systems Research Company, and Taghtiran Kashan Company.
The Iranian citizen is Parviz Khaki, who is alleged to have procured and attempted to procure goods for Iran's nuclear programme that can be used to construct, operate, and maintain gas centrifuges to enrich uranium.
"Foreign financial institutions that facilitate significant transactions to or from the sanctioned entities and individual are exposed to potential loss of access to the US financial sector. We urge financial institutions to act in a manner that preserves their access to the US financial system by cutting financial ties to these companies and individual," the State Department said in a statement.
Iranian private sector firms should heed the risks incurred by conducting business with those who support Iran's proscribed nuclear activities and should choose to focus their activities on legitimate international commerce, the State Department said.
The US will continue to investigate and research similar activities, and additional companies making material contributions to the Iranian government's proliferation of weapons of mass destruction or their means of delivery will likely be designated, it said.
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