Iran, OPEC's second-largest producer, has stopped conducting oil transactions in US dollars, a top Oil Ministry official said Wednesday, a concerted attempt to reduce reliance on Washington at a time of tension over Teheran's nuclear program and suspected involvement in Iraq. Iran has dramatically reduced dependence on the dollar over the past year in the face of increasing US pressure on its financial system and the fall in the value of the American currency. "The dollar has totally been removed from Iran's oil transactions," Oil Ministry official Hojjatollah Ghanimifard told state-run television Wednesday. "We have agreed with all of our crude oil customers to do our transactions in non-dollar currencies." 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.