TEHRAN — Iran’s Shiite leaders warned of regional sectarian conflict after reports that Syrian rebels raided a Shiite shrine in a suburb of Damascus last week, destroying the site and making off with the remains of the revered Shiite figure buried there.

It was impossible to independently verify the report, which appeared on a Facebook page on April 28. Through the course of the civil war, the Syrian government and the rebel opposition have proved adept at manipulating social media to implicate each other in atrocities, trading accusations that cannot be substantiated.

The shrine of the revered Shiite figure, Hojr Ibn Oday — also known as Hajar Ben Adi al-Kundi — in the Damascus suburb of Adra was a popular pilgrimage site before the hostilities mostly ended religious tourism in Syria. Pictures posted on Facebook seemed to show that the sanctuary had been ransacked and the remains of Mr. Oday exhumed.

The caption next to the photo reads: “This is the shrine of Hajar Ben Adi al-Kundi. It’s one of the Shiite shrines in Adra al-Balad. The heroes of the Free Syrian Army scavenged the grave and buried him in an unknown place. Praise be to God and God grant victory to the Free Syrian Army.”

The caption gives credit for the exhumation to a man named Abu Anas al-Wazir, or Abu al-Baraa, a leader of a military group called the Islam Brigade of the Free Army.

Iran’s supreme leader, Ayatollah Ali Khamenei, who considers himself a binding figure between Sunnis and Shiites, called the event “bitter and sad,” and blamed foreign intelligence agencies for the destruction of the shrine.

Iranian and Syrian students protested Monday in Tehran, shouting “death to America” and “death to Israel,” while pro-government speakers blamed Britain as a former colonizer for “sowing the seeds of discord between Sunnis and Shiites.”

The students shouted back, “Stop, stop the exhuming of graves.”

The Qaeda-inspired Al Nusra Front claimed responsibility for the abduction of the remains of Mr. Oday. The group’s attack was followed by a stern warning from Hassan Nasrallah, the leader of Hezbollah, the Lebanese Shiite militia, who on April 30 told Sunni rebels not to target the largest Shiite sanctuary in Syria, the golden-domed shrine of Sayida Zeinab, Muhammad’s granddaughter.

Mr. Nasrallah warned of “very serious repercussions” if Syrian rebels attacked the shrine, long a main pilgrimage destination for Shiites worldwide.

Such an attack would unleash an uncontrollable conflict, Mr. Nasrallah said, invoking a fearsome precedent: the destruction of a Shiite shrine in the Iraqi city of Samarra in 2006 that contributed to years of sectarian bloodletting between Shiites and Sunni Muslims there.

Fighting has engulfed areas around the Syrian shrine, which is outside Damascus, and many Shiite fighters — Syrian as well as Iraqi and Lebanese — have rushed to defend it, according to fighters interviewed in Syria.

Sunnis in the Jordan town of Southern Mazar on Friday burned down a Shiite gathering center, close to the shrine of another revered Shiite figure, Jafar Ibn Abi Talib, Iranian news media reported.

Iranian officials blamed the United States and Israel, saying they were supporting the Syrian rebels and Sunni extremist forces in the region.

“They have launched a war between Shiites and Sunnis,” Iran’s president, Mahmoud Ahmadinejad, said Sunday. “They plant bombs in Pakistan and Iraq, and recently the Zionist regime has hit Syria. We should be careful about colonizers and Israel.”

Iran’s ideological narrative is that there are no real conflicts between the sects, but that Western powers and Iran’s enemies in the region deliberately mislead certain Muslim groups. Its leaders blame ultraconservative Wahhabis and Salafists, who they say are backed by the United States and Israel, through their regional allies Saudi Arabia and Qatar.

“This Syrian so-called front, Al Nusra, is the symbol of Saudi Arabia and Qatar,” said Mojtaba Bigdeli, a former leader of a Shiite pressure group. “We respect Sunni shrines. We do not desecrate them. We may form self-sacrifice battalions to react to the Wahhabis and Salafists in Syria. For sure we will not remain silent.”