His defiance came after President Obama vowed to ratchet up global pressure on Tehran to abandon its controversial atomic program which he said indicated Iran was aiming for a weapons capability.
Iran's atomic chief Ali Akbar Salehi, meanwhile, said that plans to build one or two new uranium enrichment plants had been submitted to Ahmadinejad.
"You (world powers) can cut your own throat, jump up or down, issue statements and declarations and pass resolutions ... but don't think you can stop the progress and building of the Iranian nation," Ahmadinejad said.
"The more overt your animosity towards us, the more determined the Iranian nation will be to go forward," the hardliner said in a speech broadcast live on state television.
Ahmadinejad also reiterated that Iran had started making its own nuclear fuel for a Tehran research reactor after world powers "did not" supply the material.
"Based on the law which you wrote in the NPT (Non-Proliferation Treaty) charter, you were supposed to give the fuel for the Tehran reactor, but you did not," he said.
"We said we will do it ourselves and they made fun, but our experts did it."
The controversy over fuel for the internationally supervised reactor and Iran beginning to enrich uranium to 20-percent level have emerged as the latest points of confrontation with world powers.
On Saturday, Salehi said the construction of new uranium enrichment sites may start in the first half of the current Iranian year, which runs to March 2011.
"According to the atomic energy organization (of Iran), we will launch one or two facilities," he told the ILNA news agency.
"These facilities are dispersed in different areas of the country and they will be built at the targeted sites as Ahmadinejad sees fit."
Under a U.N.-drafted deal in October 2009, world powers proposed supplying nuclear fuel for the Tehran reactor in return for Iran's stockpiles of low-enriched uranium (LEU).
But Tehran insisted it would hand over its LEU only when it receives the nuclear fuel, with the exchange taking place inside Iran -- a condition opposed by the world powers.
Since then Washington has led global pressure on Tehran for a fourth round of U.N. sanctions, with only Beijing -- one of the five veto-wielding members of the U.N. Security Council -- still opposing this.
On Friday, Obama said global pressure on Tehran was gathering pace and warned of "huge destabilising effects in the region" if Iran acquires the capacity to make an atomic bomb.
"All the evidence indicates that the Iranians are trying to develop the capacity to develop nuclear weapons," Obama told CBS.
Iran has fiercely denied seeking to develop the bomb, saying its contested nuclear program is purely for peaceful purposes to meet the energy needs of a fast growing population.
On Friday, Obama also urged his Chinese counterpart Hu Jintao to join forces to stop Iran's atomic program. Beijing has emerged as Tehran's main economic partner and continues to press for a diplomatic solution to the crisis.
Iran's chief nuclear negotiator, Saeed Jalili, who was in China on Friday, said Beijing was heeding Tehran's calls for support.
"We jointly emphasized during our talks that these sanctions tools have lost their effectiveness," Jalili said after meeting Chinese officials including Foreign Minister Yang Jiechi.
But Jalili's remarks that he had secured Chinese backing ran counter to a growing quiet confidence among U.S. officials that Beijing was gradually being swayed over to its side.
Obama, meanwhile, also stressed he had reached out to Iran after assuming office last year to give it the option of rejoining the international community, but Tehran had only isolated itself further.
Ahmadinejad, however, said Obama had failed to make any change despite his early promises. "In reality nothing has changed ... The pressures are still on. The sanctions are still on," he said.