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Russia on Tuesday said it had written guarantees that it could carry out its work as a party to the Iran nuclear deal, suggesting Moscow could allow a revival of the 2015 pact to go forward.
Foreign Minister Sergey Lavrov's comments appeared to show Moscow retreating from its earlier view that western sanctions imposed on Russia over its invasion of Ukraine were an impediment to salvaging the nuclear deal.
Western powers said the demand was unacceptable and Washington insisted it will not provide the guarantee.
Under the deal, formally called the Joint Comprehensive Plan of Action, Iran agreed to limit its nuclear programme to make it harder to develop a nuclear bomb — an ambition it denies — in return for relief from global economic sanctions.
"We have received written guarantees," Mr Lavrov said. "They are included in the very text of the agreement on reviving the JCPOA.
"And in these texts there is a reliable defence of all the projects provided for by the JCPOA and those activities, including the linking up of our companies and specialists."
Standing alongside Iranian Foreign Minister Hossein Amirabdollahian in Moscow, Mr Lavrov denied that Russia was an obstacle to reviving the agreement.
"I have heard how the Americans have every day tried to accuse us of delaying the agreement," he said. "That is a lie.
"The agreement is not finally approved in several capitals and the Russian capital, Moscow, is not one of them."
Oil prices fell more than 6 per cent, pulled down by Mr Lavrov's comments that Moscow was in favour of the nuclear deal resuming as soon as possible, and by doubts about Chinese demand after surging Covid-19 cases in China.
But western officials said they were not sure if Russia was satisfied by guarantees it could carry out nuclear projects under the 2015 deal, or if it wanted the "right to free and full trade, economic and investment co-operation and military-technical cooperation" with Iran that Mr Lavrov sought on March 5.
US State Department spokesman Ned Price said a revival of the nuclear deal would not be "an escape hatch" for Russia to avoid sanctions imposed because of the Ukraine war.
"We, of course, would not sanction Russian participation in nuclear projects that are part of resuming full implementation of the JCPOA," Mr Price said.
"We can't and we won't, and we have not provided assurances beyond that to Russia."
Another US official responded cautiously to Mr Lavrov's comments, saying they might mean Moscow had come around to the US view that Russia's invasion of Ukraine should not mean an end to the Iran nuclear deal.
"Perhaps it is now clear to Moscow that, as we have said publicly, the new Russia-related sanctions are unrelated to the JCPOA and should not have any impact on its implementation," the senior US State Department official said.
Eleven months of fitful talks to revive the deal — which US president Donald Trump abandoned in 2018, prompting Tehran to start breaching its nuclear limits about a year later — were paused in Vienna last week after Russia demanded assurances.
Iran said the US lacked the "political will" to resolve several outstanding issues in the nuclear negotiations in Vienna.
Tehran has insisted Washington remove human rights and terrorism-related sanctions, including those imposed in 2019 on its elite Islamic Revolutionary Guard Corps.
Mr Amirabdollahian said the pause in the Vienna talks could help to resolve several of the outstanding issues and suggested that Russia was no impediment.
"If we can reach an understanding with the United States on the few issues that are our red line and get to a final agreement, Russia will stand with us until the end of talks to reach a good, stable and strong nuclear deal," he said.