Iran Foreign Minister Mohammad Javad Zarif and his deputy both reacted swiftly to US Secretary of State Antony Blinken’s remark Sunday that Tehran has not taken any step to return to its obligations under the 2015 nuclear deal, JCPOA.

“Lifting Trump’s sanctions, @SecBlinken, is a legal& moral obligation, NOT negotiating leverage. Didn’t work for trump – won’t work for you,” Zarif tweeted early Monday.

Although the Biden Administration has pledged to return to the JCPOA, which former president Donald Trump abandoned in 2018 and started talks in Vienna in April, its position has been that Iran must first stop actions that are in violation of the agreement.

Tehran insists that Washington should first lift all Trump-era sanctions. Observers believe the Vienna talks revolve around what sanctions the US is willing to lift in exchange with what sorts of concessions from Iran, but so far complicated issues have remained unresolved, according to diplomats.

Talks adjourned last week, and delegations returned for consultation, but in the meantime a temporary monitoring deal Iran had with the UN nuclear watchdog, IAEA, lapsed, so far without being replaced with a new measure to allow additional inspections of nuclear facilities.

Blinken on Sunday said the United States has not seen yet whether Iran will do what it needs to do to come into compliance with its nuclear commitments to have sanctions lifted.

"Iran, I think, knows what it needs to do to come back into compliance on the nuclear side, and what we haven't yet seen is whether Iran is ready and willing to make a decision to do what it has to do. That's the test and we don't yet have an answer," Blinken told ABC News' "This Week With George Stephanopoulos" program.

Iran began surpassing its uranium enrichment limits under the JCPOA from May 2019, when Trump intensified oil export sanctions, almost shutting off Iranian oil sales leaving the country with little foreign currency income. Oil income constitutes well over half of the government budget and the financing of its ambitions in the Middle East. A host of militant groups receive money, weapons and training by Iran’s Revolutionary Guard. Tehran’s deep involvement in Syria since 2011 and in Yemen since 2014 are not cheap ventures.

Zarif in his tweet, however, demanded concessions from the US. “Release the Iranian people’s $Billions held hostage due to US bullying,” he said, referring to Iranian funds blocked in several countries due to US banking sanctions that threaten to penalize any institution exchanging funds with Iran.

Zarif’s deputy and Tehran’s chief negotiator in Vienna, Abbas Araghchi (Araqchi) also reacted to Blinken with a tweet. “Having left JCPOA, US must first provide verifiable sanctions lifting. Iran will then resume full implementation” of the 2015 nuclear deal.

Opponents of the Biden decision to return to the JCPOA, which would require lifting some of the Trump sanctions, argue that giving Tehran a financial lifeline will enable it to continue its “malign” behavior in the region and eventually will enable it to build nuclear weapons.