"In my personal opinion, I believe the IRGC Quds Force to be a terrorist organization, and I do not support them being delisted from the foreign terrorist organization list," Joint Chiefs Chairman General Mark Milley told a congressional hearing.

Iran has pressed for the removal of the State Department's official "Foreign Terrorist Organization" designation of the Islamic Revolutionary Guard Corps as a condition for returning to the 2015 deal that sought to control its nuclear development and prevent it from acquiring a nuclear weapons capability.

The previous US administration of Donald Trump unilaterally abrogated the deal in 2018 and a year later slapped the FTO label on the Guards.

President Joe Biden has sought in negotiations to salvage the Joint Comprehensive Plan of Action, or JCPOA, as the 2015 deal is officially called.

But talks have stalled in the past month over a handful of final issues, including Iran's demand over the terror designation.

The talks are led by the State Department and Milley and the Pentagon are not directly involved.

It was not clear whether Milley was suggesting an alternative of keeping the Quds Force designated while dropping the broader Revolutionary Guards from the list.

In a statement on the original designation, the State Department said: "The IRGC -- most prominently through its Quds Force -- has the greatest role among Iran's actors in directing and carrying out a global terrorist campaign."

It singled out specific acts by the Quds Force, including attempted bombings and assassinations inside the United States and other countries.

Privately, US officials have said removing the terror designation would not have much concrete impact, because the IRGC remains under a long list of economic and political sanctions.