WASHINGTON: Reviving the Iran nuclear deal would seem like a simple task for US President Joe Biden. Iran wants him to lift sanctions in exchange for Tehran's return to compliance.

But as Iran and the United States resume indirect talks in Vienna led by the European Union, the Biden administration faces the question of which sanctions exactly are on the table.

Further casting a shadow over the talks is an explosion at a key Iranian nuclear facility purportedly carried out by Israel, a sworn foe of the 2015 accord, which led Tehran to announce it was ramping up uranium enrichment closer to weapons-grade levels.

Sweeping sanctions in place

The Joint Comprehensive Plan of Action, negotiated under former US president Barack Obama, promised Iran relief from sanctions if it drastically scaled back its nuclear program -- a commitment that UN inspectors said Tehran had been meeting.

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.