In Syria itself, “Shiites have become a main target,” said Malek, an opposition activist who did not want his last name published because of safety concerns. He was visiting Lebanon from a rebel-held Syrian town, Qusayr, where his brother died Tuesday battling Shiite guerrillas from the Lebanese militia Hezbollah. “People lost brothers, sons, and they’re angry,” he said.

The Syrian civil war is setting off a contagious sectarian conflict beyond the country’s borders, reigniting long-simmering tensions between Sunnis and Shiites, and, experts fear, shaking the foundations of countries cobbled together after the collapse of the Ottoman Empire.

For months, the fighting in Syria has spilled across its borders as rockets landed in neighboring countries or skirmishes crossed into their territories. But now, the Syrian war, with more than 80,000 dead, is inciting Sunnis and Shiites in other countries to attack one another.

“Nothing has helped make the Sunni-Shia narrative stick on a popular level more than the images of Assad — with Iranian help — butchering Sunnis in Syria,” said Trita Parsi, a regional analyst and president of the National Iranian American Council, referring to President Bashar al-Assad of Syria. “Iran and Assad may win the military battle, but only at the expense of cementing decades of ethnic discord.”

The Syrian uprising began as peaceful protests against Mr. Assad and transformed over two years into a bloody battle of attrition. But the killing is no longer just about supporting or opposing the government, or even about Syria. Some Shiites are pouring into Syria out of a sense of religious duty. In Iraq, random attacks on Sunni mosques and neighborhoods that had subsided in recent years have resumed — a wedding was recently hit — as Sunni militias fight the army.

With Sunni-led Saudi Arabia, Qatar and Turkey backing the uprising against Mr. Assad, who is supported by Shiite Iran and Hezbollah, sectarian divisions simmering since the American invasion of Iraq are spreading through a region already upended by the Arab uprisings.

The Syrian war fuels, and is fueled by, broader antagonisms that are primarily rooted not in sect but in clashing geopolitical and strategic interests: the regional power struggle between Saudi Arabia and Iran; Iran’s confrontation with the West over its nuclear program; and the alliance between Hezbollah and the secular Syrian government of Mr. Assad against American-backed Israel.

But sectarian feeling has seeped in. Iraq has been especially vulnerable. With the Sunni majority in Syria battling to overthrow a government dominated by Mr. Assad’s Alawite sect, an offshoot of Shiism, some in Iraq’s Sunni minority grew emboldened by the prospect of overthrowing their own Shiite government.

Today, many Iraqis feel they are on the road back to the dark days of 2006 and ’07, the peak of sectarian militia massacres by Shiites ascendant after years of oppression under Saddam Hussein, and by minority Sunnis disempowered by his fall.

While the 2007 American troop surge helped to limit the bloodshed, random attacks against Shiites never stopped. What was different was that the Shiites, who finally felt firmly in control of the security forces, stopped retaliating. But that seems to be changing.

Sunni militias have risen up to fight the army, and for the first time in years Sunni mosques and neighborhoods are being regularly targeted. The first notable attack was in April, at a cafe in the Sunni neighborhood of Amariya; it started late at night as young men played pool, and it left dozens of people dead. While it is unclear who is responsible for the new violence, many Sunnis blame the government, or Iranian-backed Shiite militias.

In Lebanon, perennial clashes between Alawite and Sunni militias in Tripoli have reached their worst level in years as each side blames the other for carnage in Syria.

In Syria, both the government and its opponents insist that their civil war is not a fight between religious sects. Rebel leaders say their only aim is to depose a dictator. Mr. Assad says he is fending off extremist terrorists, and he is careful not to frame the conflict as a fight against the country’s Sunni majority, which he praises for its moderation.

Mr. Assad’s affinity with Hezbollah and Iran is primarily strategic. Though his Alawite sect, about 12 percent of the population, provides bedrock support, most Alawites are secular. Syria’s fewer than 200,000 mainstream Shiites are a much smaller minority, less than 1 percent. 

BY:NEW YORK TIMES  (WWW.NYTIMES.COM )