President Barack Obama announced on Tuesday new U.S. sanctions against foreign banks that help Iran sell its oil, Reuters reported.
Obama said the measure would increase pressure on Tehran for failing to meet its international nuclear obligations.
The decision, in an executive order, came ahead of congressional votes on new sanctions intended to further strip Iran of its oil-related revenues.
It also followed criticism from Republican presidential challenger Mitt Romney that the White House is failing to act strongly enough to stop Iran's suspected pursuit of a nuclear weapon. Iran says its nuclear program is for peaceful purposes.
Obama said in a statement quoted by Reuters that the United States remains committed to finding a diplomatic resolution to the standoff with Tehran, but is also determined to step up the pressure.
“If the Iranian government continues its defiance, there should be no doubt that the United States and our partners will continue to impose increasing consequences,” he said.
The new sanctions target foreign banks that handle transactions for Iranian oil or handle large transactions from the National Iranian Oil Company (NIOC) or Naftiran Intertrade Company (NICO), two key players in Iran's oil trade.
They build on oil trade sanctions signed into law in December that have prompted buyers in Japan, South Korea, India and China to significantly cut their purchases to avoid penalties.
The new executive order has the same rules, providing "exceptions" to countries that have demonstrated significant cuts.
Iran's currency has plunged since the United States and European Union first targeted its oil revenues this year, making it harder for Tehran to spend money on its nuclear program, and ramping up internal political pressures within the country, said Ben Rhodes, a national security adviser to Obama.
“The proof of the success of the approach can be seen in the data, that you have up to a million barrels of oil a day that are off the market from last year,” Rhodes was quoted by Reuters as having told reporters.
Obama's order also targets China's Bank of Kunlun and Iraq's Elaf Islamic Bank for providing services to Iranian banks.
The order came one day after negotiators from the Senate and House of Representatives agreed upon a bill that would impose new sanctions aimed at further restricting Iran's oil revenues.
Reuters reported that the House is expected to vote on the bill on Wednesday. A Senate vote on the sanctions is expected to happen before Congress breaks at the end of the week for an extended recess.