Iran on Tuesday accused Western parties to its 2015 nuclear deal of "persisting in their blame game", a day after European diplomats warned the pact would soon be an empty shell if not revived.
"Some actors persist in their blame game habit, instead of real diplomacy. We proposed our ideas early, and worked constructively and flexibly to narrow gaps," Iran's top negotiator, Ali Bagheri Kani, said on Twitter.
"Diplomacy is a two-way street. If there's real will to remedy the culprit's wrongdoing, the way for a quick, good deal will be paved."
In a pessimistic assessment of talks between Iran and major powers in Vienna, diplomats from Britain, France and Germany warned on Monday that "time is running out" to rescue the pact, which they said would very soon become "an empty shell" without progress in negotiations.
Indirect talks between Iran and the United States started in April but stopped in June after the election of hardline cleric Ebrahim Raisi, whose negotiating team has returned to Vienna after five months with an uncompromising stance.
The stakes are high. Failure in the negotiations would carry the risk of a new regional war, with Israel pushing for a tough policy if diplomacy fails to rein in Iran's nuclear work.
In 2019, Iran started breaching nuclear restrictions under the pact in response to a decision in 2018 by then U.S. President Donald Trump to withdraw from the agreement and reimpose harsh sanctions that have devastated Iran's economy.
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"Who violated the deal? Americans. Who should compensate for that and be flexible? Americans of course," said a senior Iranian official.
Iran's clerical rulers believe that a tough approach, spearheaded by their strongly anti-Western Supreme Leader Ayatollah Ali Khamenei, can force Washington to accept Tehran's "maximalist demands", analysts and diplomats said.
"But it could backfire. This is a very dangerous and sensitive issue. Failure of diplomacy will have consequences for everyone," said a diplomat in the Middle East.
During the seventh round of talks, which began on November 29, Iran abandoned any compromises it had made in the previous six, pocketed those made by others, and demanded more, a senior U.S. official has said.
With significant gaps remaining between Iran and the United States on some key issues – such as the speed and scope of lifting sanctions and how and when Iran will reverse its nuclear steps – chances of an agreement seem remote.
Iran insists on immediate removal of all sanctions in a verifiable process. The United States has said it would remove curbs "inconsistent" with the nuclear pact if Iran resumed compliance with the deal, implying it would leave in place others such as those imposed under terrorism or human rights measures.
Iran also seeks guarantees that "no U.S. administration" will renege on the pact again. But Biden cannot promise this because the nuclear deal is a non-binding political understanding, not a legally binding treaty.
"How can we trust Americans again? What if they ditch the deal again? Therefore the party that violated the deal should provide guarantees that it will never happen again," said the Iranian official.
"This is their problem not ours to solve ... They can find a solution and give us guarantees."