Iranian President Mahmoud Ahmadinejad called the depreciating dollar a "worthless piece of paper" at a rare summit last year in Saudi Arabia attended by state leaders from the Organization of Petroleum Exporting Countries.
Iran put pressure on other OPEC countries at the meeting to price oil in a basket of currencies, but it has not been able to generate support from fellow members — many of whom, including Saudi Arabia, are staunch U.S. allies.
The U.S. briefly had two aircraft carriers in the Gulf on Tuesday amid a rotation of forces. Defense Secretary Robert Gates said the deployment serves as a "reminder" to Iran, though he said it was not an escalation of force.
U.S. banks are prohibited from conducting business directly with Iran, and many European banks have curbed their dealings with the country over the past year under pressure from Washington.