Peace negotiations with Iran fell apart after Tehran severely misjudged what kind of leverage the regime believed it held, a U.S. official told Fox News Digital on Sunday.While Vice President JD Vance left Islamabad, Pakistan, without a deal between the U.S. and Iran, the official said Vance used the talks to measure the Iranians own assessment of their position in the negotiations.Vance found that Tehran thought they held a strong hand going into negotiations, according to the official, who added that no deal can be achieved when one party deludes itself into believing they have leverage that, in reality, they do not have.GEN JACK KEANE 'SKEPTICAL' THAT IRAN CEASEFIRE WILL HOLD, WARNS TEHRAN WILL 'DELAY AND OBFUSCATE'The U.S. official described the talks to Fox News Digital as starting out tough, though developing into a more friendly and productive dialogue over the duration of the 21-hour-long negotiations.The high-stakes talks between the U.S. and Iran ended without a deal after Iranian officials refused to accept American terms, Vance said earlier Sunday during a press conference from the Serena Hotel in Islamabad, Pakistan."So we go back to the United States, having not come to an agreement. We've made very clear what our red lines are, what things we're willing to accommodate them on and what things we're not willing to accommodate them on," Vance said at the time. "And we've made that as clear as we possibly could, and they have chosen not to accept our terms."TRUMP REVEALS IRAN MADE 'SIGNIFICANT PROPOSAL' AFTER ULTIMATUM, BUT 'NOT GOOD ENOUGH'The U.S. official said that over the course of the discussions, the Washington delegation determined it was clear that the Iranians did not comprehend that the core of any peace deal hinges on Iran never obtaining a nuclear weapon.While that point remains the main objective of any potential peace deal, the U.S. has other red lines that it will not compromise on.The official said the U.S. and Iran failed to reach an agreement on all of Washingtons red lines, which include: Iran ending all uranium enrichment; the dismantling of all Irans major nuclear enrichment facilities; the retrieval of highly enriched uranium; the acceptance of a broader peace, security and de-escalation framework that includes regional allies; an end to the funding of Irans terrorist proxies Hamas, Hezbollah and the Houthis; and Iran fully opening the Strait of Hormuz with no tolls for passage.The official added that Vance has underscored that while a deal remains on the table, it is up to Tehran to accept the terms."And we leave here with a very simple proposal, a method of understanding that is our final and best offer," Vance said during the earlier press conference before departing Pakistan. "We'll see if the Iranians accept it."