Iranian Foreign Minister Mohammad Javad Zarif delivered a message on YouTube that Iran was ready to take steps to ensure its nuclear programme remains peaceful but would not "kneel in submission" to do a deal with major powers.
As talks to resolve the long-running nuclear stand-off resumed in Vienna, Zarif's remarks, delivered on Wednesday in English in a five-minute video, appeared to be a response to a US warning that Tehran has yet to prove that its atomic ambitions are peaceful.
The statements highlighted how much work the negotiators from Iran and from the United States, France, Germany, Britain, China and Russia still have to do to meet a self-imposed deadline of July 20. The sixth round of talks since February between Iran and the six powers were due to formally get under way in Vienna yesterday.
Washington and some of its allies have imposed sanctions on Iran over suspicions that its nuclear programme is designed to produce weapons - a charge denied by Iran, which says it is only interested in producing electricity and other peaceful projects.
In the video, Zarif said a nuclear deal would make history, and Iran was "willing to take concrete measures to guarantee that our nuclear programme will always remain peaceful".
But he added: "To those who continue to believe that sanctions brought Iran to the negotiating table, I can only say that pressure has been tried for the past eight years - in fact for the past 35 years.
"It didn't bring the Iranian people to kneel in submission. And it will not now, nor in the future."
July 20 is the expiry date of an interim accord that grants Iran modest relief from economic sanctions in return for some curbs on its atomic work, but Western officials acknowledge that an extension is looking increasingly likely.
In an article in The Washington Post, US Secretary of State John Kerry said Iran's "public optimism about the potential outcome of these negotiations has not been matched, to date, by the positions they have articulated behind closed doors".
But Iranian Deputy Foreign Minister Abbas Araqchi told Iranian media the fact that almost three weeks had been scheduled for final negotiations was "a sign the two sides are serious about driving the talks to a conclusion".