On Monday the UN Security Council ordered Iran to halt uranium enrichment and other sensitive nuclear fuel work by August 31 or face the prospect of sanctions.
But the hard-line president has told a rally of citizens in the north-eastern town of Bojnurd that it was their right to exploit peaceful nuclear fuel cycle technology.
"If some people think they can talk to us with a language of force and threats, they are making a bad mistake. If they don't realise that now, one day they will learn it the hard way," Mr Ahmadinejad warned.
Iran insists it wants to enrich uranium only to make reactor fuel and that this is a right enshrined in the nuclear Non-Proliferation Treaty (NPT).
Demands for a suspension stem from widespread suspicions the country wants the capacity to make weapons-grade uranium.
Mr Ahmadinejhad made no direct comment on the resolution but other senior officials dismissed it as "destructive" and "worthless".
"This resolution will definitely have no constructive results and could only worsen the situation," foreign ministry spokesman Hamid Reza Asefi said, quoted by the official IRNA news agency.
"It has only been designed to pressure Iran and to prematurely block the path of negotiations," he added.
Parliament Speaker Gholam-Ali Hadad-Adel was quoted by the ISNA news agency as saying: "While the security council does not dare to condemn the Qana massacre (in south Lebanon) ... it feels alarmed by Iran's nuclear activities and adopts a resolution that is worthless in the eyes of the people."
Iran's ambassador to the United Nations said the resolution was "destructive and totally unwarranted".
"I would suggest to you that this approach will not lead to any productive outcome. It can only exacerbate the situation," Javad Zarif told the security council in New York.
The security council charged International Atomic Energy Agency (IAEA) chief Mohammed ElBaradei with reporting back on Iranian compliance.
The resolution was pushed through after Iran ignored a previous non-binding deadline and failed to respond to the offer of a package of incentives in exchange for a moratorium on nuclear fuel work.
But the text held off from an immediate threat of sanctions, which have been opposed by Russia and China, and said any punitive action would have to be the subject of further discussions.
US Secretary of State Condoleezza Rice said she was "confident that we have very good cooperation with Russia and China on this issue", while asserting that the resolution "does not close the door to diplomacy".