TEHRAN, Iran >> Iran’s Foreign Minister Mohammad Javad Zarif suddenly resigned late today without warning, offering an “apology” to the nation as the nuclear deal he negotiated with world powers stands on the verge of collapse due to the U.S. withdrawal from the accord.

The 59-year-old veteran diplomat first offered a vague Instagram post with an “apology” for his “inability to continue to his service.” The post included a drawing of Fatima, the daughter of the Prophet Muhammad.

A Foreign Ministry spokesman, Abbas Mousavi, told the state-run IRNA news agency minutes later that Zarif had resigned, without offering any reason for his departure.

Zarif’s resignation leaves Iran’s relatively moderate President Hassan Rouhani without one of his main allies in pushing the Islamic Republic toward more negotiation with the West. Analysts have said Rouhani faces growing political pressure from hard-liners within the government as the unraveling nuclear deal further strains the country’s long-weakened economy.

The U.S.-educated son of a wealthy family, Zarif overcame hard-line objections and Western suspicions to strike the accord with world powers that saw Iran limit its enrichment of uranium in exchange for the lifting of crippling economic sanctions.

The deal, though, later faced a challenge from the administration of President Donald Trump, who pulled America out of the accord, while fueling doubts of those at home still wary of U.S. interests decades after Iran’s 1979 Islamic Revolution. Zarif himself faced withering criticism at home once for even shaking hands with President Barack Obama.