"These entities and individuals were designated because they provide the Iranian government goods, technology and services that increase Iran's ability to enrich uranium and/or construct a heavy water moderated research reactor," State Department spokeswoman Victoria Nuland said.
"Given Iran's continued intransigence on its nuclear program... it is essential to act to restrain continued Iranian violations," she said.
Among the five people targeted was Fereidoun Abbasi-Davani, the head of the Atomic Energy Organization of Iran (AEOI), and an expert in nuclear isotope separation.
He had been involved in stepping up "activities related to uranium mining and the production of yellowcake" which is needed for uranium enrichment, Nuland said in a statement.
Morteza Ahmadali Behzad, the managing director of the Iran Enrichment Company, was also fingered "for his role in making complex and sensitive centrifuge components."
The companies which were targeted included Aria Nikan Marine Industry which has supplied magnetic tape for use in centrifuges, the Iranian-government owned Iran Pooya, which manufactures aluminum cylinders, and Faratech, involved in developing a heavy water research reactor.
Under the sanctions imposed by the State Department and Treasury, American businesses are barred from conducting any business with the designated firms and individuals.
"We hope those financial institutions will act in a manner that preserves their access to the US financial system by cutting financial ties to these nuclear support companies," Nuland added.