President Obama is moving forward with toughened sanctions against Iran's oil exports after determining there is enough crude on the world market to allow U.S. allies to stop purchasing Iranian oil, the White House said today.

"I determine… that there is a sufficient supply of petroleum and petroleum products from countries other than Iran to permit a significant reduction in the volume of petroleum and petroleum products purchased from Iran by or through foreign financial institutions," the president wrote in a memo to the departments of Energy, State and Treasury.

"I will closely monitor this situation to assure that the market can continue to accommodate a reduction in purchases of petroleum and petroleum products from Iran," he said.

Today's announcement is a precursor to sanctions against foreign banks that purchase Iranian oil, a move which is intended to isolate Iran's central bank and reduce its oil revenues.

The White House would not comment today on how the sanctions might impact gas prices, which have spiked in recent months.

"I'm not going to speculate about oil prices and how they move in part because global oil prices are set in a global market and are affected by a variety of factors," a senior administration official said.

White House Press Secretary Jay Carney admitted in a written statement that the global oil market is "tight."

"Nonetheless, there currently appears to be sufficient supply of non-Iranian oil to permit foreign countries to significantly reduce their import of Iranian oil," Carney said.