Saudi Arabia and Iran’s increasingly bitter dispute about Islamic pilgrimages to Mecca escalated after a senior Iranian cleric publicly called Saudi custodianship of Islam’s two holiest sites as "servitude" and called for their "emancipation." Ayatollah Javadi Amoli, speaking to an Iranian seminary class, also denounced the Saudi government’s ongoing military campaign in Yemen, Iranian media reported Thursday.

“The custodianship of [Mecca and Medina] should be handed to men of piety,” Amoli, an influential Shiite Muslim scholar, said in comments reported by the semi-official state news agency Mehr. “The current Saudi custodians however are the [descendents] of those who turned it to a house of idols and indulged themselves in drunken revelry,” he said, adding that the conditions of the holy cities’ custodianship should be reviewed with the aim of freeing them “from the servitude” of the Sunni monarchy.

Harsh rhetoric between the two regional rivals is far from uncommon and has heated up in recent months against the backdrop of the Saudi-led airstrike campaign targeting Iranian-backed Shiite rebels, known as Houthis, in Yemen. However, Amoli’s call hits a sensitive spot for Saudi Arabia’s rulers, who have historically derived much of their regional credibility from their custodianship of Mecca, the birthplace of Islam that all able-bodied Muslims are required to make a pilgrimage to once in their lifetime.

“Saudi Arabia bases its whole legitimacy on religion,” said Ali Al-Ahmed, a Saudi expert and the director of the Institute for Gulf Affairs in Washington. “Because the Saudis control Mecca, they have been able to make themselves a great regional player.” The importance of Mecca and Medina, Islam’s second-holiest city, to the Saudi monarchy is underscored by the official title claimed by the kingdom’s rulers. Every Saudi king since 1986 has officially been called the “Custodian of the Two Holy Mosques,” in reference to Mecca’s al-Haram mosque and Medina’s al-Nabawi mosque.

Control of the holy cities has historically been an important tool not only for political legitimacy but as a means of elevating its rulers to represent all Muslims, according to Madawi Al-Rasheed, a visiting professor at the Middle East Center in the London School of Economics. “Mecca was and continues to be the jewel in the Arab crown,” Al-Rasheed wrote in a commentary for Al-Monitor. “Without it, the Saudi leadership would be just one regional power among many others.”

In recent years, the kingdom has used its position as the gatekeeper of the holy cities as an effective political tool, leveraging access to minimize criticism of its government by Muslims and to retaliate against critics, Al-Ahmed said. This tendency appears to be particularly true where Iran is concerned. The current dispute between the Saudi government and Iran around the pilgrimages was sparked by allegations that Saudi authorities sexually harassed two teenage Iranian male pilgrims. Tensions were later exacerbated when the kingdom turned away an Iranian plane carrying 260 pilgrims on the grounds that it did not have permission to use the country’s airspace. Iran suspended all pilgrimages to the country on Monday in response.

Amoli’s call for the emancipation of the mosques has some precedent in a particularly dark period in relations between the two countries. The last time such a high-ranking Iranian official publicly disavowed Saudi Arabia’s custodianship of the holy sites was in the contentious aftermath of the 1987 bloodshed in Mecca that left 400 pilgrims, mostly Iranians, dead after Saudi security forces cracked down on an unauthorized protest at the holy site. Following the incident, Iran broke off diplomatic relations with the kingdom and boycotted the pilgrimage for several years, while prominent figures began calling for the transfer of Saudi control of Mecca.

The calls for emancipating Mecca and Medina from Saudi control come at a time when the political tensions between the two states are dialing up, both from the Yemen conflict and as the recently signed nuclear agreement between Iran and world powers adds to Saudi Arabia's and its Gulf allies’ concerns about the Islamic Republic’s regional hegemony.