US Republican Senator Joni Ernst has joined many other lawmakers calling on President Joe Biden to leave the Vienna nuclear negotiations with Iran.

In a tweet on Thursday, Ernst said that “the Iranian regime’s funding of terrorism and hatred of the United States has not changed”.

Reviving the 2015 Iran nuclear deal remains uncertain despite earlier progress US officials reiterate, as the issue of delisting Iran's Revolutionary Guard (IRGC) as a terrorist organization remains unresolved.

Earlier, White House national security adviser Jake Sullivan said, "We've made progress over the course of the last several weeks. There are still some issues left", adding that whether there would be a closure or not was unclear.

The number of lawmakers and former officials from both sides of the isle who are urging the Biden administration to walk out of the talks has been growing in recent days.

Spearheading the efforts are Republican lawmakers who have issued numerous statements and letters to stop Washington from removing the IRGC from the US list of foreign terrorist organizations in the framework of the new agreement.

They say the IRGC is a terrorist organization that is not going to change its ways and stop destabilizing the region, and a nuclear deal with the Islamic Republic that lifts sanctions would simply release money for Tehran to support its proxy militants in the region.