Iran has denied any slowdown.
On Sunday, Ahmadinejad said: "They [world powers] thought that by issuing any resolution Iran would back down. But after each resolution the Iranian nation took another step along the path of nuclear development.
"Now it has put into operation more than 3,000 centrifuges and every week we install a new series."
A UN atomic energy agency report released last week has said that Iran was still short of 3,000 centrifuges.
The report said that, as of August 19, Iran had a total of 1,968 centrifuges operating at its uranium-enrichment plant in the central town of Natanz.
A total of 656 more centrifuges were said to be under development.
Western powers have accused Iran of seeking to build atomic weapons.
They are particularly concerned about progress in the country's uranium-enrichment programme because the process can be used to make fuel for power plants or, if desired, nuclear weapons.
Two sets of sanctions have already been given to Iran for its failure to obey a UN demand to stop enrichment activity.
The US, leading efforts to isolate Iran, has said that Tehran faces a third if it does not stop the work.