"Pressure of some Western countries to force Iran to abandon its right (to nuclear technology) will not get a result," the Iranian state-run news agency, IRNA, quoted President Mahmoud Ahmadinejad as saying.
The White House said Mr Ahmadinejad's remarks were just a "negotiating position" and urged Iran to study a basket of incentives, approved by the US, British, French, German Russian and Chinese foreign ministers at a Vienna meeting, before officially responding.
European officials will give Iranian officials a detailed presentation of the incentives in the next couple of days and a formal answer is hoped for within weeks, White House spokesman Tony Snow said.
However President Ahmadinejad's comments suggested Tehran may have already decided to reject offers of incentives and negotiations from six of the world's top powers in return for ending atomic fuel activities.
Although President Ahmadinejad did not mention uranium enrichment, Mohammad Saeedi, deputy head of Iran's Atomic Energy Organisation, said Iran's plans included such sensitive work.
"Iran is determined to go ahead with its nuclear enrichment work for peaceful purposes," he told students' news agency ISNA.
US response
US Secretary of State Condoleezza Rice still held out the possibility she would meet Iranian officials in what would be the highest-level such face-to-face contact since the 1979 Islamic revolution. Washington cut ties with Iran in 1980.
"It depends of course on what Iran does," she told National Public Radio in one of a series of interviews. Washington says Iran must stop atomic fuel work before any talks.
"If Iran is prepared to verifiably suspend its program and enter into negotiations, then we'll determine the level (of representation), but I wouldn't be at all surprised if the ministers meet at some point," she said.
Iran was facing a "moment of truth", she told CBS.
Russian reaction
Russian President Vladimir Putin said it's too early to speak about sanctions against Iran.
"As far as sanctions are concerned, we think it is a bit too early at the moment to talk about that," Mr Putin said at a meeting with the chiefs of international news agencies in Moscow.
"We need to have a deep conversation with the Iranian leadership. Only after that can we talk about the next step."
But Ms Rice said Moscow and Beijing had signed up in Vienna to two "quite robust" paths - one leading Iran to international integration with incentives and another towards isolation via various penalties.
"Russia and China have signed on to the two paths," she told CNN.
A European Union diplomat said Russia and China, both major trading partners of Iran, had agreed not to block any UN sanctions against Tehran, but could opt out of particular punitive measures.
"There is something like a catalogue of sanctions and we can pick and choose from them. The agreement reached ... is also that Russia and China can abstain from any sanctions, but not say no," the diplomat said on condition of anonymity.
Western officials would not say if the package specified what sanctions Iran could face, but Russia said military action, raised by Washington as a last-resort option was not currently on the table.