Washington announced it imposed additional sanctions on Iran's proliferation networks and front companies used to evade sanctions on the country's energy sector.
David Cohen, undersecretary of state for terrorism and financial intelligence, said Iran is under "intense" sanctions pressure, though additional measures are needed to address longstanding concerns about Iran's nuclear program.
"Today's actions are our next step on that path, taking direct aim at disrupting Iran's nuclear and ballistic missile programs as well as its deceptive efforts to use front companies to sell and move its oil," he said in a statement.
The U.S. State Department said it identified companies based in the United Arab Emirates, Switzerland, China and Malaysia as front organizations for the National Iranian Oil Co., among others.
U.S. Secretary of State Hillary Clinton announced in late June China and Singapore have met the requirements to get an exemption, bringing the number of exempted countries to 20. Countries that "significantly" cut back on the amount of crude oil imported from Iran are protected from U.S. sanctions.
Iranian Energy Minister Madjid Namjou was quoted by the official Islamic Republic News Agency as saying tightened sanctions have little impact on the country.
"Sanctions and the international pressures against Iran have resulted in country's self-sufficiency in implementing major power projects," he said.