Iranian Foreign Minister Mohammad Javad Zarif stepped down on Monday, announcing his resignation on Instagram, reports Aljazeera.
"I am apologising you for all the shortcomings ... in the past years during my time as foreign minister ... I thank the Iranian nation and officials," he wrote on his Instagram page jzarif_ir.
There was no immediate reason giving for the resignation.
Iran's state-run IRNA news agency cited a spokesman, Abbas Mousavi, confirming Zarif had resigned.
Zarif was appointed minister of foreign affairs in August 2013, two years before Iran agreed to scale back its uranium enrichment programme and pledged not to develop nuclear weapons in return for the lifting of international sanctions as part of a landmark nuclear deal brokered with the United States, the UK, France, Germany, Russia, China and the European Union.
A vocal supporter of the deal, Zarif has since come under pressure from more hardline power blocs within the Islamic Republic who were opposed to the agreement, formally known as the Joint Comprehensive Plan of Action (JCPOA).
Criticism of the accord has become more intense in recent months following US President Donald Trump's decision in May to withdraw from the deal and reimpose sanctions on Tehran.
Trump's decision prompted Iran's currency, the rial, to crater raising sporadic nationwide protests.
Visibly frustrated Hassan Abbasi, a retired general in Iran's hardline Revolutionary Guard, gave a speech earlier this month saying he believed Iranian people would spit on Zarif and other Iranian officials - including President Hassan Rouhani and member of parliament Ali Larijani - who backed the nuclear deal.
"Mr Hassan Rouhani, Mr Zarif and Mr Larijani, go to hell," Abbasi said at a demonstration in the Iranian city of Karaj.
A staunch Rouhani ally, Zarif - normally collected - appeared visibly frustrated at times during a recent security conference in Munich.
Already lashed by criticism over the collapsing nuclear deal and renewed tensions with the US, the relatively moderate Rouhani faces anger from Muslim leaders, hardline forces, and an ever-growing disaffected public.
Rouhani is particularly vulnerable because of the economic crisis assailing the country's currency, which has hurt ordinary Iranians and emboldened critics to openly call for his removal.
Rouhani secured the 2015 nuclear deal after two years in office and won the praise of Iranians, who flooded the streets to celebrate it. Under the agreement, Iran limited its enrichment of uranium in exchange for the lifting of economic sanctions.
But the benefits of the deal never reached much of the Iranian public.
Even before Trump pulled out from the accord in May 2018, uncertainty over its future caused the rial to plummet.