(CNN) As attempts to revive the 2015 Iran nuclear deal heat up, Tehran is seeking guarantees that it will be compensated if a future US president pulls out of the pact, a regional diplomat told CNN on Tuesday.
Last week European Union officials sent the US and Iran what it called the "final text" of a revived deal to limit Tehran's nuclear program in exchange for sanctions relief.
On Monday night, Iran responded to the proposal in writing, meeting a deadline set by the bloc. While Iran's written response has not been made public, the country's chief adviser to negotiations tweeted that an agreement was closer than ever, but not yet done.
But the regional diplomat, who has been briefed on the matter, said Iran has reservations about the possibility of a future president pulling out of the deal and unleashing new sanctions on the country -- in what would be a repeat of the May 2018 decision by former US President Donald Trump to leave the agreement and impose crushing financial penalties on Tehran.
"It seems there has been progress in bringing views closer, especially in the issue of indirect sanctions on Iranian companies working abroad," the diplomat said.
"The main issue facing the revival of the deal is the guarantees requested from the Iranian side ensuring Iran will be compensated in case future US administrations decide to withdraw again from the deal and while no real solution has been put forth," he added.
An adviser to the Iranian negotiating team at talks on the deal in Vienna, Mohammad Marandi, confirmed to CNN on Tuesday that Iran was looking for guarantees that if a future US administration withdraws from the deal, it will "have to pay a price."
Marandi also said in a tweet on Monday that there were "differences" on two other issues, but declined to offer specifics.
CNN is seeking comment from the US State Department.
The negotiations between the US and Iran are currently being negotiated by Qatar and the EU. Qatar's deputy Foreign Minister Mohammed Al Khulaifi was sent to Tehran over the weekend for meetings with Iran's negotiator Ali Bagheri Kani.
An EU spokesperson, Nabila Massrali, confirmed that Iran's response had been received on Monday night and that the bloc was now in consultation with the US and other participants of the deal, formally known as the Joint Comprehensive Plan of Action (JCPOA).
The US called on Iran on Monday to drop "extraneous" demands that go beyond the JCPOA's scope -- namely in reference to an earlier Iranian request that the US remove Iran's elite Islamic Revolutionary Guard Corps (IRGC) from its Foreign Terrorist Organizations list.
"If Iran wants these sanctions lifted, they will need to alter their underlying conduct; they will need to change the dangerous activities that gave rise to these sanctions in the first place," the State Department spokesperson Ned Price said in a Monday briefing.
In the wake of the US withdrawal, Iran has increasingly violated the agreements it made under the deal and expanded its nuclear program.
Iran has said any final deal should protect the rights of the country and guarantee the lifting of sanctions, which could free up tens of billions of dollars in oil and gas revenue and boost Iran's struggling economy.
Earlier on Monday, Iran's Foreign Minister Hossein Amir-Abdollahian said if the US showed a realistic and flexible reaction to Iran's offer, they "would be at the point of agreement."
Amir-Abdollahian said Tehran was ready to reach a conclusion through a foreign ministerial meeting and announce the final agreement if its views were accepted. "The upcoming days are important days," he said.
Last week, a State Department spokesperson told CNN that the US was "ready to quickly conclude a deal on the basis of the EU's proposals."