Just across the border from the war in Syria, in a house in the Turkish town of Reyhanli, Ismail Mohamed, a rebel soldier in a T-shirt and camouflage pants, opens his laptop and proudly displays a video. The video shows Mohamed sitting with two forlorn captives in the back of a van, glaring at them and contemptuously patting them on the cheek. The van was in Syria, Mohamed says, but the men are fighters from Iran. He is sure of it—so sure, he says, that he hadn’t thought to show their Iranian ID cards on camera before he handed his captives over to Turkish authorities. To him, their presence is just more proof that the rebels are fighting not only President Bashar al-Assad, but also his allies in Tehran. “We’re fighting against something very important,” he says, “the expansion of the Iranian revolution.”

In recent weeks, Assad has watched his regime suffer a string of setbacks—from a bombing in Damascus that killed four members of his inner circle to a constant stream of defections, including that of his handpicked prime minister, who fled to Jordan last week. The rebels have even launched offensives in Syria’s two largest cities, Damascus and Aleppo. Nevertheless, Assad pushes on, pounding the rebels with tanks and fighter jets. Despite claims that the regime’s days are numbered, Assad’s persistence has lent credence to fears that the Syrian war will be a long bloody struggle—and that as it drags on, outside forces will come to play a larger role in shaping the country’s fate. To many rebels, the principal enemy is Iran, which has “bet the pistachio farm on Assad” in hopes that Syria will remain a political ally, says Karim Sadjadpour, a senior analyst at the Carnegie Endowment for International Peace. “Iran is trying to buoy Assad with financial, military, and strategic aid. But Iran is stealth and tends to operate via proxy.” To the rebels, murky signs of Iranian meddling already abound. Last week, the rebels captured a busload of 48 Iranians outside Damascus who they say are members of the Revolutionary Guards. The regime has insisted that they’re just religious pilgrims, but according to The Wall Street Journal, the group booked their trip through a travel agency that “solely caters to members and families of Guards.” Meanwhile, in the Turkish border camp that houses the brass of the Free Syrian Army, the main rebel fighting force, rumors have swirled that Iranians are pouring into Aleppo. Gen. Mustafa Sheikh, the head of the FSA military council, told Newsweek that he believes Iranian snipers have been hiding on the city’s rooftops. “They’re in groups with Syrian security officers, so the Iranians can remain unseen,” he said.

On their part, the Iranians are painting the war as a wider international struggle against their man in Damascus. On a visit to the Syrian capital last week, a senior aide to Ayatollah Ali Khamenei, Iran’s Supreme Leader, went out of his way to warn that the Syrian uprising was “not an internal issue.” The aide appeared to be referring to a host of Iranian foes, including the United States, Turkey, and Qatar, all of which are publicly backing the rebels. But the longer the fighting continues, the greater the potential for Syria to become an arena for a larger struggle between Iran and its main regional rival, Saudi Arabia. Some among the Syrian opposition feel that such a battle is already taking place. As one veteran Syrian activist, Nasr Adin Ahmad, put it: “This revolution, it’s just like a chess piece between Iran and Saudi Arabia.”‬