"Nothing about our overall approach to Iran has changed. We continue to pursue a strategy of deterrence, of pressure and diplomacy," Blinken told reporters.

"We've been clear that Iran must de-escalate to create space for future diplomacy," he said.

EU-mediated talks to restore a 2015 nuclear deal, scrapped by former president Donald Trump, broke down last year in a dispute over sanctions relief and amid massive, women-led protests against the clerical state.

Blinken said that the United States remained "committed to ensuring that Iran never acquires a nuclear weapon" and would hold Iran "accountable for its human rights violations" and "destabilizing actions."

Iran has moved five US citizens from prison to house arrest in a first step of a deal announced last week for their release.

South Korea in turn will unfreeze $6 billion in Iranian oil revenue frozen out of concern for US sanctions, transferring the money to an account in Qatar aimed at humanitarian purchases.

Republican rivals swiftly denounced the deal as enriching an enemy, but Blinken insisted Iran would only gain access to money that was already its own.