(Bloomberg) -- Iran rejected at talks last week the “very detailed outlines” of an arrangement the US was willing to accept to revive the 2015 nuclear accord, a top US diplomat said. 

Robert Malley, the US Special Envoy for Iran, told National Public Radio that recent negotiations in Doha amounted to “more than a little bit of a wasted occasion.” 

Efforts to restore the nuclear agreement, which limited Iran’s atomic work in return for sanctions relief, are hanging by a thread. The contours of a deal were drawn at multi-party talks in Vienna but progress stalled in March as the US and Iran disagreed on whether and when to ease penalties not directly linked to the nuclear pact, which then-President Donald Trump exited in 2018.

They include Iran’s demand that the US remove the Islamic Revolutionary Guard Corps, a powerful military organization, from its list of terrorist groups. Congressional opposition to that move has weighed on US President Joe Biden as elections loom later this year.

Iran Nuclear Tensions Risk Boiling Over in Middle East: IAEA

Biden has sought for more than a year to revive the deal. During that time, he’s maintained Trump-era sanctions on the country and Iran has rapidly expanded its nuclear work while steadily dialing down international oversight, making it increasingly difficult to convince US lawmakers and regional allies to support an agreement.

The nuclear watchdog warned on Tuesday that the lack of progress in verifying Iran’s nuclear program may have an impact on the broader region.

“The party that has not said yes is Iran,” Malley told NPR. In Doha, Iran “added demands that I think to anyone looking at this would be viewed as having nothing to do with the nuclear deal, things that they’ve wanted in the past that clearly us and the Europeans and others have said that’s not part of this negotiation.” 

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