"We will use all our potential with regard to uranium enrichment for progress in the prosperity of Iran," Ahmadinejad said in a speech in Khorassan province in north-eastern Iran.
"There was no way the world powers could stop our momentum or threaten us," the president added in his speech, carried live by the news network Khabar.
He rejected the world powers' charges that Iran was working on nuclear weapons as "baseless."
"We are not after the atomic bomb because our people are the real bomb and if you (world powers) should plan to harm us, then these very people would smash you," Ahmadinejad said.
"We would welcome shaking any hand if offered out of goodwill but if trying to harm Iran, the hand and arm would be cut off," he added.
Ahmadinejad said that as the world powers were politically and economically at a dead end, "they would have no future without (the cooperation of) Iran."
"We are a reasonable country and would welcome constructive cooperation with the world but we will not accept any bullying and will not tolerate an imperialistic approach," Ahmadinejad said.
Tehran said earlier Tuesday that world powers should not be worried about the new phase of Iran's nuclear programs.
Iran's atomic chief Ali-Akbar Salehi said Monday that in the new Persian year, which begins March 21, the country planned to build two new uranium enrichment sites inside a mountain to protect them from a possible attack.
European Union foreign ministers said that they were running out of patience with Iran over its nuclear programme, and the US State Department said the plans were further evidence that Iran refused to engage cooperatively and constructively.
"The world powers should not be worried as all our nuclear activities are strictly supervised by the inspectors of the International Atomic Energy Agency (IAEA)," Foreign Ministry spokesman Ramin Mehmanparast said in a press briefing in Tehran.
The spokesman reiterated that Iran's nuclear activities were solely for peaceful purposes and blamed certain countries for politicising the issue by raising absurd charges about Iran pursuing a secret military programme.
Atomic chief Salehi said long-term plans call for 10 new enrichment sites to be built, followed by 10 more in the future.
Locations for five sites have already been found, and the remaining five were to be decided soon, he said.
Mehmanparast also said Iran was still ready to accept a deal with Russia and France to swap low-enriched uranium for fuel to be used in the Tehran medical reactor.
But the spokesman reiterated Tehran's position that the swap should be made on Iranian soil, and rejected any third country as a venue for the exchange.
He said the Tehran medical reactor was to be used for cancer treatment, and rejected any political considerations that would delay the fuel supply.