There were reportedly three shipments of one centrifuge each from the black-market network of disgraced Pakistani nuclear scientist Abdul Qadeer Khan in 1997, one diplomat said.
Centrifuges are used to enrich uranium for either nuclear reactor fuel or atom bomb material.
Iran, which already has the less high-tech P-1 centrifuges, denies having received the more advanced machines, which make enriching uranium easier.
Tehran says its nuclear program is a peaceful effort to generate electricity but the United States alleges it is hiding covert work on atomic weapons, for which highly enriched uranium is necessary.
A second diplomat said the UN watchdog International Atomic Energy Agency (IAEA), which has been investigating Iran’s nuclear program for three years, was investigating the P-2 report.
Asked if this could be the "smoking gun" for the West’s fears, the diplomat replied: "Yes. If this is confirmed the game is over."
The diplomat did not rule out that the shipments could have contained more than one centrifuge.
Iran claims it only received designs for P-2 machines in the mid-1990s and "that it did not pursue any work on the P-2 design between 1995 and 2002," an IAEA report in September 2005 noted.
The first diplomat, who like other envoys interviewed asked not to be named due to the sensitivity of the issue, said a former member of AQ Khan’s network had told Western interrogators that "there were three actual shipments to Iran of one P-2 each three separate times in 1997."
Non-proliferation analyst David Albright told AFP from Washington that the Khan network "always sent sample machines with designs."
"It would make sense if Iran got this. This is how the Khan network worked. They had stockpiles of these things in Dubai," said Albright, a former UN nuclear inspector.
If Iran "imported whole P-2 machines, that’s a significant difference from what they told the IAEA," he said.
Iranian officials in Vienna could not be reached for comment.