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demanded Monday the removal of all sanctions in a verifiable process as abandoned by Washington three years ago.

In a statement published just before the talks started, said: "The United States still fails to properly understand the fact that there is no way to return to the deal without verifiable and effective lifting of all sanctions imposed on the Iranian nation after the USÌýdeparture."

"The return of the USÌýto the nuclear deal would be meaningless without guarantees to prevent the recurrence of the bitter experience of the past," he said, adding that "this opportunity is not a window that can remain open forever".Ìý

International after a five-month hiatus with Tehran "determined" to reach a deal.Ìý

Iran paused the negotiations in June after the election of an ultraconservative new presidentÌý. Diplomats at the time had said they were "close" to an agreement.

Iran ignored appeals from Western countries to restart the talks for several months, all the while strengthening the capabilities of its nuclear programme. In August, Raisi said Iran was again open to talks.

The talks started just after 3 p.m. (1400 GMT) in the Palais Coburg hotel where the 2015 agreement - known as the Joint Comprehensive Plan of Action (JCPOA) - was clinched.

Along with Iran, diplomats from Britain, China, France, Germany and Russia are attending.

is taking part in the talks indirectly.