Venezuelan President Hugo Chavez declared today the "empire of the dollar is crashing".
Mr Chavez, who on Saturday said oil prices could double to $200 per barrel if the US attacks Iran over its disputed atomic programme, was speaking after talks with Iranian president Mahmoud Ahmadinejad.
"Soon we will not talk about dollars because the dollar is falling in value ... naturally, by the crash of the dollar, America's empire will crash," Mr Chavez said.
Both presidents, who have consistently denounced US influence in the world, attended an Opec summit at the weekend, advocating a move away from the dollar as the international trading currency for oil.
After the summit they said they would press for action which could include pricing oil in a basket of currencies. Mr Ahmadinejad called the dollar a "worthless piece of paper."
However, the final statement of the oil cartel's summit in the Saudi capital Riyadh did not include any reference to the falling dollar, in an apparent victory for US-allied moderates led by Saudi Arabia.
The dollar's fall on global markets helped fuel oil's rally to a record $98.62 earlier this month - causing the West to call for more Opec supplies to cool prices - but it has also eroded the purchasing power of Opec members.
Fears the US or its ally Israel could attack Iran - over a nuclear energy programme Washington says is a cover for seeking atomic weapons - have also contributed to higher crude prices.
Tehran insists its nuclear programme is for power generation.