President Ahmadinejad's announcement on Thursday came despite warnings from the West that resuming atomic research would endanger efforts to find a diplomatic compromise over Iran's nuclear ambitions.
"Recently, some of them have said the Iranian nation has no right to nuclear research," Ahmadinejad said in a speech to thousands of people in the holy city of Qom broadcast on state television.
"But they should know that the Iranian nation and government will defend the right to nuclear research and technology and will go forward prudently.
"By relying on its young scientists, Iran will use this technology for medicine, industry and energy in the near future."
Ahmadinejad's speech was greeted with cries of "Ahmadinejad, our hero, we support you" from the crowd.
Iran's announcement on Tuesday that it would resume nuclear research and development, suspended more than two years ago, brought swift warnings from Washington and the European Union, which fear that Tehran is secretly building nuclear weapons.
Western diplomats said Iran's latest announcement, which followed its resumption of uranium conversion in August, was likely to increase calls for Iran's case to be referred to the UN Security Council for possible sanctions.
"if it [the Holocaust] is not true and it is a big historical lie, why are you imposing such a corrupt and brutal regime on the nations in this region?"
Mahmoud Ahmadinejad, the president of Iran
Iran says it will use nuclear technology only for peaceful purposes, such as electricity generation, and that as a signatory of the nuclear Non-Proliferation Treaty (NPT) it has a right to do so.
Ahmadinejad also defended his recent proposal that Israel be moved to Europe on the ground that during World War Two, it was Jews, not Palestinians, who were killed by Europeans.
"Why should the Palestinian nation pay the price for your crimes?" he said. "Give a piece of your country to them [Israelis], and let it be finished. There is no need for meetings, conferences, peace treaties and so on.
"And if it [the Holocaust] is not true and it is a big historical lie, why are you imposing such a corrupt and brutal regime on the nations in this region?
"As soon as I asked this question, you said that Ahmadinejad is a war-monger and is against human rights, so we should not allow his nation and government to have access to nuclear technology.
"Be sure that not only the Palestinian nation, but all Islamic nations, will not tolerate this occupier-regime [Israel] in the region for a minute."