Mr. Rubaie explained what Shiites believe would happen if the Assad government were toppled by Sunnis: “We expect that the blood would run heavy in Iraq if they held power in Syria, because they think that Shiites are infidels and our lives, our money and our women are permissible for them to take, and that killing us is one of the requirements to enter paradise.”

As Western and Arab governments consider actions to stop the bloodshed — options that have been explored include more aggressive diplomacy, arming the rebels or military intervention — those discussions have been encumbered by a lack of cohesion among the Syrian opposition, evidence that some of the rebels may be affiliated with Al Qaeda and credible reports of sectarian killings.

At the core of the unity problem is an issue of sectarian identification. Sunni radicals with the Islamic State of Iraq, an umbrella group that includes the local branch of Al Qaeda, have urged fighters to go to Syria, which makes it harder for the West to embrace the opposition. Recently the group released a statement on its Web site calling for new violence against Shiites here in Iraq, according to the SITE Intelligence Group, which monitors the communications of jihadist groups.

Syria’s minorities have the example of Iraq in considering their own future, should the Assad government fall: Assyrian Christians, Yazidis and others were brutally persecuted by insurgents. In Egypt, where a similar paradigm was toppled with the long-serving dictator Hosni Mubarak, Christians have experienced more sectarian violence, increasing political marginalization and a growing link between Islamic identity and citizenship.

“Christians are all saying that Syria risks becoming the new Iraq, a country divided among ethnic and religious lines where there is no place for Christians,” said the Rev. Bernardo Cervellera, the editor in chief of AsiaNews, a Catholic news agency. Syria, while not a democracy, “at least protects them,” he said.

Abu Ali recalled hearing anti-Shiite slogans chanted in Homs by rebels in opposition to Syria’s alliance with Iran, which, like Iraq, is a majority-Shiite state in a region that is predominantly Sunni. He heard calls for “Christians to go to Beirut,” and “Alawites to the grave.”

In Najaf on a recent Sunday, Abu Ali sat on a couch in the office of a local religious leader who had taken him in. Outside, chickens roamed the narrow streets lined by flat-roofed concrete homes, jostling for space with women covered in black abayas and security men who guarded the office with assault rifles.