The Iranian delegation departed the venue for high-level negotiations with the United States in Switzerland, effectively halting the talks.
The walkout was triggered by a social media post from US President Donald Trump, which Iranian officials described as insulting.
Mediators issued a statement confirming the conclusion of the session without a final agreement.
This development marks a sharp reversal in momentum for the diplomatic effort aimed at securing a permanent end to the conflict between the two nations.
The talks, which had been progressing through Swiss mediation, focused on broader regional stability, including the situation in Lebanon.
The interruption highlights the persistent volatility of the negotiation process, where political signaling from Washington can rapidly derail technical progress.