U.S. President Barack Obama has signed an executive order that carries out new sanctions against Iran that Congress approved and that he signed this summer.
The sanctions seek to deter Iran from pursuing a nuclear weapons program, as many Western governments suggest it is doing.
Iran insists its nuclear development is for peaceful purposes.
White House National Security Council spokesman Tommy Vietor says stepped-up sanction aimed at Iran have "produced profound and demonstrable results."
Congress in August passed legislation that would expand sanctions to target individuals or companies who issue or purchase Iranian debt or who assist the Iranian government in the development or transportation of Iranian oil or its petrochemicals.
The International Monetary Fund (IMF) this week predicted that Iran's economy would shrink by 0.9 percent in 2012, in part due to international sanctions efforts that have targeted Iranian oil revenues.
But the IMF, whose forecast is based on what some say are questionable figures provided by Tehran, also suggested Iran would tame runaway inflation and get back to growth in 2013.
Iranian authorities have also been battling to prop up the Iranian currency, the rial, which has lost much of its value this year and sparked a recent crackdown on moneychangers.
Based on reporting by AP, Reuters, and AFP