The remarks by two Iranian officials before Thursday's talks come as America assembles its biggest deployment of aircraft and warships into the Middle East in decades, part of Trump's efforts to get a deal while Iran struggles at home with growing dissent following nationwide protests in January.
If the negotiations fail, Trump has threatened to attack Iran - something Mideast nations fear could spiral into a new regional war as the embers of the years-long Israel-Hamas war still smoulder.
Already, Iran has said all US military bases in the Mideast would be considered legitimate targets, putting at risk the tens of thousands of American service members in the region.
Trump on Tuesday in the US gave his annual State of the Union speech, touching on Iran and the nuclear negotiations.
"They've already developed missiles that can threaten Europe and our bases overseas, and they're working to build missiles that will soon reach the United States of America," Trump said.
"They were warned to make no future attempts to rebuild their weapons program, and in particular nuclear weapons, yet they continue. They're starting it all over."
Iran long has maintained its nuclear program is peaceful.
The West and the International Atomic Energy Agency say Iran had a nuclear weapons program until 2003.
It had been enriching uranium up to 60 per cent purity before the June attack - a short, technical step away from weapons-grade levels of 90 per cent.
Responding to Trump, Iranian foreign ministry spokesman Esmail Baghaei sought to compare him to Joseph Goebbels, Adolf Hitler's propaganda minister.
He accused Trump and his administration of conducting a "disinformation and misinformation campaign" against Iran.
"Whatever they're alleging in regards to Iran's nuclear program, Iran's ballistic missiles, and the number of casualties during January's unrest is simply the repetition of 'big lies'," Baghaei wrote on X.
Trump said in his speech at least 32,000 people were killed in the protests, which is at the further end of estimates offered by activists for the death toll.
Mohammad Bagher Qalibaf, Iran's parliament speaker, separately said the US could either try diplomacy or face Iran's wrath.
"If you choose the table of diplomacy - a diplomacy in which the dignity of the Iranian nation and mutual interests are respected - we will also be at that table," Qalibaf said, according to the semi-official Student News Network.
"But if you decide to repeat past experiences through deception, lies, flawed analysis and false information, and launch an attack in the midst of negotiations, you will undoubtedly taste the firm blow of the Iranian nation and the country's defensive forces."
Iran and the US are due to meet on Thursday in Geneva, Switzerland, their third round of talks under the mediation of Oman.
If the talks fail, uncertainty hangs over the timing of any possible attack, as well as its mission and goals.
If the aim is to pressure Iran to make concessions in nuclear negotiations, it's not clear whether limited strikes will work.
If the goal is to remove Iran's leaders, that will likely commit the US to a bigger, longer military campaign.
The status of Iran's nuclear program is another mystery.
Trump earlier said American strikes "obliterated" it, but now, dismantling whatever remains of the program appears to be back on the administration's agenda.
IAEA inspectors have not been allowed to inspect those sites and verify what remains.
