Iranian Foreign Minister Javad Zarif stands on the balcony of Palais Coburg, the venue for nuclear talks in Vienna, Austria, July 2, 2015. Image Credit: Reuters

Iranian Foreign Minister Javad Zarif, who led his country's nuclear negotiations with world powers, signaled that his surprise decision to resign was because he was undermined in his role.

In his first public comments after Monday's announcement, Zarif said he hoped the move would eventually allow the ministry "to return to its rightful place in foreign policy." President Hassan Rouhani hasn't yet accepted Zarif's resignation.

About 150 Iranian lawmakers, or a third of the chamber, signed a letter addressed to the president petitioning to keep Zarif in his role, state-run media reported.

Zarif's resignation and public comments highlight the struggle of moderate Iranian politicians to engage with the West in the face of hardline opposition at home and aggressive U.S. policies. President Donald Trump last year pulled the U.S. out of the landmark 2015 nuclear agreement that was supposed to herald an end to Iran's international isolation.

The resignation coincided with a visit from Syria's President Bashar Al Assad to Tehran, where he met with Supreme Leader Ayatollah Ali Khamenei as well as Rouhani. Pictures posted online suggested Zarif wasn't present at the meetings.

The timing led analysts to speculate that Iran's top diplomat was being sidelined on key foreign policy issues, such as the country's role in propping up Assad's government after nearly eight years of civil war in Syria.

Divisions have also been apparent on other matters such as the future of the nuclear program abandoned by the U.S. Rouhani's government has said the country needs to abide by the accord despite U.S. sanctions. Hardline groups within the ruling establishment suggest Iran should free itself from the limitations imposed by the deal.

Deal Champion

A U.S.-educated career diplomat, Zarif led Iran's negotiating team during lengthy talks with the U.S. and other world powers that culminated in the 2015 Joint Comprehensive Plan of Action, or "Iran deal,' which lifted some sanctions against the Islamic Republic in exchange for commitments on its nuclear enrichment program. Trump pulled the U.S. out of the accord and reimposed sanctions, leaving Iran to try and salvage what it could of the agreement.

A post shared by Javad Zarif (@jzarif_ir) on Feb 25, 2019 at 11:51am PST

Brokering the deal made Zarif popular with reformists and moderates in Iran's fractious political system, but he was also the subject of criticism from the Islamic Republic's hard-liners, who are traditionally suspicious of any engagement with Washington and Europe. The U.S. withdrawal has emboldened the hard-liners and weakened Rouhani, who has been trying to come up with ways to retain some of the benefits of the agreement in negotiations with other signatories.

U.S. Secretary of State Michael Pompeo remarked on Zarif's resignation in a tweet: