In a televised speech, Mahmoud Ahmadinejad said on Thursday that Tehran would not approve the language of threats.
"They [the West] should know that the Iranian nation will not yield to pressure and will not accept any violation of its rights," Ahmadinejad told a crowd of thousands in Orumiyeh in northwestern Iran.
Iran has repeatedly said uranium enrichment, which the United Nations has demanded it stop, is its legitimate right to have access to nuclear technology for peaceful purposes, and will not be abandoned.
"Arrogant powers want to stop our nation's progress... I am telling them that they are wrong," Ahmadinejad said.
The UN security council had set an August 31 deadline, demanding Tehran halt uranium enrichment or face possible sanctions.
Mohamed ElBaradei, head of the Vienna-based International Atomic Energy Agency (IAEA), will report to the council later in the day to certify whether Iran has suspended "all enrichment-related and reprocessing activities, including research and development".
The world's fourth largest oil exporter insists it wants nuclear technology only to cope with booming electricity demands, but some say the programme is a smokescreen for producing atomic weapons.
"They [the West] should know that Iranian nation will not yield to pressure and will not accept any violation of its rights"
Mahmoud Ahmadinejad, the president of Iran
Washington says world powers are poised to begin discussing punitive measures against Iran if, as expected, the IAEA finds Tehran ignored a UN security council demand to stop enriching uranium by August 31.
As time was running out, Iran vowed never to drop the project and launched one of its key elements, a heavy-water plant.
Iran says it is pursuing a peaceful programme permitted by the nuclear non-proliferation treaty to generate energy and has denounced pressure for an unconditional suspension as illegal.