Last week, dozens of prominent Sunni clerics in Saudi Arabia signed onto an online statement that called for a jihad in Syria against foreign invaders. It urged Arab states to "give all moral, material, political and military" support to Islamist factions fighting the regime of Syrian President Bashar al-Assad, who is buttressed by Russian and Iranian support.

"The Western-Russian coalition with the Safavids" — a reference to a once mighty Persian Shiite dynasty — "and the Nusairis" — a reference to Assad's Alawite sect, deemed apostate by some Sunni fundamentalists — "are making a real war against the Sunni people and their countries," the statement read.

The Syrian civil war has entered its fifth year. It has claimed the lives of some 300,000 Syrians, forced half the country's population to flee their homes and led to the steady, calamitous unraveling of one of the Middle East's more complex, multiconfessional states.

The 53 Saudi clerics behind the deeply sectarian call to arms were not affiliated with the Saudi government and, unlike other state-sanctioned declarations, did not directly criticize the Islamic State or Jabhat al-Nusra, al-Qaeda's affiliate in Syria. The urgency of their message is a reflection of the escalating conflict in Syria, which has seen Russia now aggressively intervene on behalf of the Assad regime.

"The holy warriors of Syria are defending the whole Islamic nation. Trust them and support them," the statement reads, urging the strengthening of rebel factions, "because if they are defeated, God forbid, it will be the turn of one Sunni country after another." It goes on, peddling anti-Christian rhetoric while denouncing Russians as "fanatical people of the Cross."

Bruce Riedel, a Middle East analyst at the Brookings Foundation, likens the call to the days when Saudi Wahhabi clerics inveighed against the Soviet invasion of Afghanistan. "The statement reflects the growing intensification of sectarian extremism in the region," he writes. "The Sunni-Shiite war has been escalating for the last few decades but it is now boiling at a fever pitch."

The hardline clerics are far from the only ones involving themselves in matters of war. Recently, the Imam of the Holy Mosque of Mecca participated in a conspicuous act of military propaganda, firing an artillery gun in the direction of Houthi rebels in Yemen.

This week, as my colleague Loveday Morris reported, Nusra leader Abu Mohammed al-Jolani called on followers to launch reprisal attacks on Russian soil in retribution for the intervention.

"The new Russian invasion is the last arrow in the quiver of the enemies of the Muslims," Jolani said in an audio recording, calling on Muslims in Russia's restive Caucasus to strike both civilian and military targets.

"If the Russian soldier kills from the masses of [Syria], kill from their masses," he said. "And if they kill from our soldiers, kill from theirs. One for one."

As WorldViews noted earlier, there's also a religious narrative to Russia's role in the Middle East. In a previous era, the czars in Moscow styled themselves as protectors of the Middle East's Christians; the recent Russian air war won the swift backing of the country's Orthodox Church, which said the offensive was part of a "sacred battle."

Meanwhile, Shiite passions have also been on display. In Lebanon, hundreds gathered to mourn a prominent Hezbollah commander who died fighting alongside Syrian regime forces in Idlib province.

On Sunday in Tehran, thousands turned out for the funeral for Brig. Gen. Hossein Hamedani, a senior figure in Iran's Revolutionary Guards, who was believed to have been killed near the Syrian city of Aleppo.

Iran's state media said Hamedani was "killed by Takfiri terrorists," a pejorative reference to Sunni Muslims.