The Treasury Department designated Kalaye Electric Co., Kavoshyar Co. and Pioneer Energy Industries Co., freezing their US assets and barring Americans from dealing with them.

"Treasury is taking this action to deny Iran access to the materials and services that support its nuclear ambitions," said Stuart Levey, Treasury under secretary for terrorism and financial intelligence.

He said the designation was "consistent with our international obligations under UN Security Council Resolution 1737," which imposed sanctions on Iran for its failure to halt uranium enrichment.

The latest action intensified a US government squeeze on Iranian banks and companies. Last month, Treasury blacklisted Iran's fifth largest bank, Bank Sepah, for allegedly helping finance the country's illicit weapons programs.