The Middle East's two great geopolitical adversaries entered into a war of words ahead of the annual Hajj pilgrimage to Mecca, which starts this weekend.
Their rivalry, shaped by sectarian Sunni-Shia divisions, can be seen in numerous bloody proxy conflicts across the region. But it also flares up in heated rhetorical broadsides.
The latest round began with comments from Iran's Supreme Leader, Ayatollah Ali Khamenei, who in full bluster condemned the Saudis for prohibiting Iranian pilgrims from joining the Hajj after talks about security and logistics collapsed.
Last year's pilgrimage was marred by the deaths of hundreds of pilgrims caught in a stampede with more than 2000 killed, according to one unofficial tally, although the Saudis say the death toll is lower.
Khamenei ventured that the slain devotees, including many Iranian nationals, lost their lives either because of Saudi complicity or incompetence. (He errs towards the former.)
"Saudi rulers ... who have blocked the proud and faithful Iranian pilgrims' path to the Beloved's House, are disgraced and misguided people who think their survival on the throne of oppression is dependent on defending the arrogant powers of the world, on alliances with Zionism and the US," Khamenei said in a statement posted on his official website on Tuesday.
"The world of Islam, including Muslim governments and peoples, must familiarise themselves with the Saudi rulers and correctly understand their blasphemous, faithless, dependent and materialistic nature," the statement went on, asserting that the kingdom's rulers were unfit to be the custodians of Islam's holiest sites.
"Because of these rulers' oppressive behaviour towards God's guests, the world of Islam must fundamentally reconsider the management of the two holy places and the issue of Hajj."
A day later, Saudi Arabia's top cleric, Grand Mufti Abdulaziz Al Sheikh, fired back, dismissing Khamenei's criticism as a feature of supposed Iranian hatred toward Sunnis.
Iran's theocratic regime sees itself as the vanguard of Shia Islam, similar to how the Saudis, practitioners of a particular orthodox Wahabist brand of the faith, style themselves as the leaders of the Sunni world.
The grand mufti pointed to the pre-Islamic history of what's now Iran, where the bulk of population were once fire-worshipping Zoroastrians, and suggested that this ancient legacy still shadowed the present.
"We must understand they are not Muslims, for they are the descendants of Majuws" - a term for Zoroastrians - "and their enmity toward Muslims, especially the Sunnis, is very old," he said.
Such language has dangerous echoes. So much of the recent bloodletting in the Middle East has been justified on arguments of apostasy and treachery to the faith. Iran and Saudi Arabia's governments find themselves on opposite ends of wars in Iraq, Syria, Lebanon and Yemen - battles where the most aggressive actors frame their campaigns in sectarian terms.
Iranian Foreign Minister Javad Zarif responded to Al Sheikh's remarks with a tweet, linking Saudi Wahabism to the fundamentalist terrorism of the moment: "Indeed; no resemblance between Islam of Iranians & most Muslims & bigoted extremism that Wahhabi top cleric & Saudi terror masters preach."
But the Saudis themselves cast the Iranians as international pariahs, bent on fomenting armed struggle and terrorist plots around the world. Zarif's Saudi counterpart, Adel al-Jubeir, said in a speech last week that the regime in Tehran "is behind some of the operations threatening national security of the region".
He added: "We wish from Iran, a great nation with great history and great people, to be able to change its policies which it built in 1979 so it can be a new member in the international community, weaving new policies with it."