The International Atomic Energy Agency said it had evidence Iran was conducting theoretical work aimed at developing a nuclear weapon. Tehran, however, maintains its nuclear program is peaceful.
Washington announced it was placing sanctions on entities working with Iran in its petroleum sector. The Treasury Department said sanctions would be triggered if a single transaction in the Iranian petroleum sector was valued at $1 million or more than $5 million in a 12-month period.
Tehran said through the official Islamic Republic News Agency that methods to get around major sanctions would "become more elaborate."
Ali al-Saffar, an analyst at the Economist Intelligence Unit in London, told Bloomberg News that Washington threw up an "extra road block" to scare investors from Iran but noted the U.S. government didn't want to take Iranian crude completely off the market.
The International Energy Agency estimates Iran gets about $80 billion per year from its 3.5 million barrels of oil exported from the country. It ranks second behind Saudi Arabia in terms of oil production and has some of the largest natural gas deposits.
The British and Canadian governments announced similar sanctions in response to the IAEA report.