TEHRAN, Feb. 25 (CGTN) -- Iranian Foreign Minister Mohammad Javad Zarif, who was the lead negotiator in the 2015 nuclear deal, announced his resignation on Instagram on Monday, which can only take effect once President Hassan Rouhani accepts it.

"I apologize for my inability to continue serving and for all the shortcomings during my term in office," Zarif said in a message posted on his verified Instagram account.

Zarif thanked Iranians and "respected officials" for their support "in the last 67 months."

The resignation of Iran's top diplomat was confirmed by an informed source. However, Rouhani's chief of staff strongly denied reports that the president had accepted Zarif's resignation in a tweet.

The resignations happened hours after a surprise visit by Syrian President Bashar Al-Assad to Tehran. However, according to the semi-official ISNA News Agency, Zarif was not present at any of Assad's meetings with Iran's supreme leader Ayatollah Ali Khamanei and Rouhani.

Prominent members of parliaments immediately called for Rouhani not to accept the resignation.

"Undoubtedly the Iranian people, government and state will not benefit from this resignation," said Mostafa Kavakebian, a reformist MP.

"A great majority of MPs demand that the president never accept this resignation," he said in a tweet.

The head of parliament's influential national security and foreign policy commission told ISNA how a planned trip to Geneva with Zarif on Monday afternoon had been canceled at the last minute with no explanation.