Iran's chief nuclear negotiator said on Saturday Tehran expects U.S. sanctions on oil, banks and most individuals and institutions to be lifted based on agreements so far in Vienna talks, Iranian media reported, while Washington again played down the prospect of an imminent breakthrough.

"Sanctions ... on Iran's energy sector, which include oil and gas, or those on the automotive industry, financial, banking and port sanctions, all should be lifted based on agreements reached so far," Deputy Foreign Minister Abbas Araqchi was quoted as saying by Iranian state media.

Araqchi did not say under which mechanism sanctions would be lifted or refer to how Tehran would meet Washington's demands and return to its commitments under the deal.

"We will negotiate until the two sides' positions come closer and our demands are met," he said. "If they are met there will be an agreement, if not there will naturally be no agreement."

Asked to comment, the U.S. State Department referred back to past statements, including remarks on Friday from U.S. National Security Adviser Jake Sullivan, who said the talks were in "an unclear place."

"We've seen willingness of all sides, including the Iranians, to talk seriously about sanctions relief restrictions and a pathway back into the JCPOA," Sullivan said, referring to the Joint Comprehensive Plan of Action, the nuclear deal's title.

"But it is still uncertain as to whether this will culminate in a deal in Vienna," he said.

Senior diplomats from the so-called E3 - France, Britain and Germany - said in a statement: "We have much work, and little time, left. Against that background, we would have hoped for more progress this week."

Officials have said they hope to reach a deal by May 21, when an agreement between Tehran and the UN nuclear watchdog on continued monitoring of some Iranian nuclear activities is due to expire. 

Russian side expressed "cautious and growing optimism" and saying they hoped to achieve concrete results within three weeks.

The deal, which curbs Iran's nuclear program in exchange for sanctions relief, has been on life support since then U.S. President Donald Trump bolted in 2018.

Representatives of the parties still in the agreement who met for just over an hour noted the "indisputable progress" achieved, Russian ambassador Mikhail Ulyanov said on Twitter, adding that he was cautiously optimistic.

"It's too early to be excited, but we have reasons for cautious and growing optimism. There is no deadline, but participants aim at successful completion of the talks in approximately three weeks. Is it realistic? We will see," he wrote.

(With input from Reuters and AFP)