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Obama's successor Donald Trump called the JCPOA "the worst deal ever" and withdrew in 2018, saying the accord did not take into account other objectionable activities by Iran.

Trump imposed a unilateral embargo on Iran's key export of oil, punishing any other country that bought it.

Trump went on to impose a number of additional sanctions including declaring Iran's powerful Revolutionary Guards to be a terrorist group, the first time such a designation has been given to a state entity.

Openly seeking to tie Biden's hands, the Trump administration in its final months announced a number of duplicative restrictions such as designating Iran's central bank for alleged terrorist financing in addition to previous nuclear sanctions.

A senior US official reiterated after the initial talks in Vienna last week that Biden was ready to lift "all sanctions that are inconsistent with the JCPOA."

"It's not as easy a process as it may sound precisely because the Trump administration went out of its way to make it difficult for a successor administration to rejoin the JCPOA," the official said.

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