Iranian President Mahmoud Ahmadinejad on Thursday dismissed any new UN sanctions resolution as "a torn piece of paper" that would not stop Tehran's nuclear work, the official IRNA news agency reported.
"Issuing such torn pieces of paper ... will not have an impact on Iranian nation's will (to obtain nuclear technology)," IRNA quoted Ahmadinejad as telling a rally in central Iran.
US, British, French, German, Russian and Chinese diplomats at the United Nations have reached a tentative deal on imposing fresh sanctions on Iran and hope to introduce the measure at the Security Council on Thursday, providing their governments agree.
An earlier sanctions resolution passed by the Security Council in December was derided by Ahmadinejad in similar terms.
Senior Iranian leaders, including the country's most powerful figure Supreme Leader Ayatollah Ali Khamenei, have all ruled out halting uranium enrichment, which can produce fuel for use either in nuclear bombs or civilian power stations.
But many moderate politicians have blamed Ahmadinejad's defiant rhetoric for pushing Iran toward international isolation and want a less confrontational approach.
Two prominent Iranian reform parties have urged the government to suspend enrichment to preserve what they call the national interest, a reference to avoiding isolation that could hurt the economy. Officials brush off economic worries.
The new UN resolution, which may be adopted next week, would impose extra penalties on Iran for refusing to halt enrichment.
"What is the aim of issuing such resolutions? Today we are mastering the nuclear fuel cycle completely," Ahmadinejad said.
"If all of you (Westerners) get together and call your ancestors from hell as well, you will not be able to stop the Iranian nation."
The West fears Iran's atomic work is aimed at building atomic weapons. Iran, the world's fourth largest oil exporter, denies it.
Ahmadinejad said imposing sanctions on Iran would be counter-productive.
"You sanctioned us in the past but we obtained the nuclear technology. Impose economic sanctions on us today and see what would be our next step," Ahmadinejad said.
He said Western powers were wrong to suppose Iran would give up its nuclear program under political pressure, adding that the Security Council had "no legitimacy".
All the Iranian nation insists on this right and will not retreat one iota," Ahmadinejad said.
Washington says it would prefer a diplomatic solution to the crisis but does not rule out military options.
Iran's chief nuclear negotiator Ali Larijani warned on Wednesday that Iran would respond militarily if Iran was attacked over its nuclear program.