Marathon talks to revive the Iran nuclear deal have met a new roadblock, with Iran accusing the United States of refusing to make the political decisions needed to enshrine the deal in international law or expand the scope of the economic sanctions that would be lifted.

The issue has hampered talks in Vienna between the West, Russia, Iran and China – which have been ongoing since February – from the start. There is no sign that the eighth round of negotiations, once intended to be the final round, has achieved the breakthrough some expected.

Ali Shamkhani, the hardline secretary of Iran’s National Security Council, in a tweet posted in multiple languages, said after speaking to his government’s negotiators that progress was becoming “increasingly difficult”.

Expressing his frustration with the delays, he said: “The Vienna negotiations had reached a point where the outcome could be described definitively without the need for guesswork.

“A US political decision to accept the deal or to refrain from accepting the demands of a credible and lasting agreement based on the principles accepted in the nuclear deal can replace speculation.”

The United States, he said, has continued to come up with new initiatives primarily designed to evade its commitments.

Foreign Ministry spokesman Saeed Khatibzadeh in his weekly press conference tried to calm the mood by saying he had spoken to Iran’s chief negotiator in Vienna, Ali Bagheri, and that he had been assured that the position was “neither flowers nor nightingales, nor rocks and thorns”. But, he added, it is incumbent on the United States to agree to the terms from Iran.

Asked what guarantees Iran was seeking, Khatibzadeh said: “The United States is not trustworthy and therefore objective guarantees must be obtained so that international law and relations are not further flouted by the US government.

He added that all sanctions should be lifted at the UN Security Council. “It doesn’t matter what the title of the sanctions is since they were applied under a false label,” Khatibzadeh said.

He stressed that any agreement on the release of political prisoners, including US dual nationals held in Iranian prisons, was only discussed in parallel with the nuclear talks.

Professor Mohammad Marandi, an Iranian analyst in Vienna considered close to the government, also said tensions centered on the range of sanctions that would be lifted under the deal. Iran is pushing for all sanctions to be lifted, but the United States says some sanctions are related to human rights abuses and terrorists, and are unrelated to the nuclear deal.

Mikhail Ulyanov, the Russian ambassador to the talks, adopted a less pessimistic tone. He said talks were at a final stage and “significant progress” had been made. But he has tended to take a more positive view, adopting a close role as mediator between the United States and Iran, a role he has maintained despite tensions over Ukraine. Wang Qun, China’s ambassador to the UN in Vienna, also broke silence over the weekend to say the talks were in their final stages.

The 20-page draft deal with annexes is largely written, but the outstanding issues show the Iranian regime’s absolute determination to ensure it appears to emerge victorious from the talks, having withstood the might of US sanctions .

Joe Biden, distracted by the Ukraine crisis, is already facing growing political resistance from Republican US senators who insist the president cannot evade Congress by refusing to put any new deal to a vote. Democrats have said that if the deal goes to the Senate for approval, they don’t think the necessary 60 senators will vote to reject it. The Senate is split 50/50, with Vice President Kamala Harris having the casting vote.

But the Iranian military’s recent demonstration of new long-range solid-fuel missiles with a range of 900 miles (1,450 km) will do little to help the US administration sell the deal.

Iran has also claimed that the US negotiating team – with which it does not meet directly – is divided on the degree of compromise.

The deal is designed to bring the United States, and then Iran, back into the original nuclear deal signed in 2015, from which the United States withdrew in 2018.

The talks were held amid repeated warnings from the West going back months that the talks can only continue for a few more weeks as Iran moves ever closer to securing irreversible peace. material and knowledge necessary to manufacture a nuclear weapon.