Iran's Supreme Leader Ayatollah Khamenei has said the framework deal reached with the US last week offers "no guarantee" of any final agreement over his country's nuclear program.
In comments made on his official website and posted to his Twitter account, Khamenei said he was "neither for nor against" the deal, explaining: "It's all about the details.The disloyal side may want to stab #Iran in the back over the details;It is too early to congratulate."
"What's been done so far secures neither the main deal nor its contents nor is it even clear whether #talks will bear fruit & lead to a deal," he added.
The comments will cast further doubt on the framework deal, which was lauded by US President Barack Obama but has since been the subject of confusion and disputes with Tehran over the details - including most notably how and when sanctions on Iran will be removed.
The Iranians want the sanctions removed as soon as the deal comes into effect, while the White House is insisting they would need to be "rolled back" gradually, with mechanisms in place to allow them to be "snapped back" if Iran is seen reneging on the deal.
But Khamenei insisted it was the Americans who were untrustworthy, despite his regime's long history of lying to and deceiving inspectors.
"I trust our negotiators but I'm really worried as the other side is into lying & breaching promises; an example was White House fact sheet," he said, referring to a disputed explanation of the details published by the US.
"Hours after the #talks, Americans offered a fact sheet that most of it was contrary to what was agreed.They always deceive &breach promises.
"All #sanctions should be removed just when the deal is reached. If sanctions removal depends on another process then why we started to talk?" he added, echoing comments made by Iranian President Hassan Rouhani earlier today.