Beirut - Potentially the most unstable country in the Middle East, Lebanon for the most part has stayed on the sidelines of the Arab Spring, keeping up appearances as an oasis of relative modernity, commerce and good times.

But the spillover effects of the Syrian war are ripping off that thin veneer.

Beneath the surface lurk the same forces that devastated the country during its years of civil war, with simmering hatreds still dividing Muslims and Christians, Sunni and Shiites, and secular and fundamentalist groups. Outside forces are still arrayed, militias are still armed and the country seems forever on the verge of tearing itself apart.

"Of all Syria's neighbors, Lebanon is the weakest, the most political and ideologically polarized and split among sectarian lines," said Fawaz A. Gerges, head of the Middle East Center at the London School of Economics. "The fear is not if the Syrian conflict will spill over - but whether it has already reached the streets of Beirut."

The assassination of Lebanon's intelligence chief in a car bomb Friday is threatening to upend a fragile political balance in Lebanon, a country plagued by decades of strife - much of it linked to political and military domination by Damascus.

The funeral for Brig. Gen. Wissam al-Hassan descended into chaos over the weekend as soldiers fired tear gas at protesters who tried to storm the government palace. The demonstrators were furious at a leadership they consider beholden to Syria, blaming al-Hassan's death on the regime in Damascus. Al-Hassan, 47, was a powerful opponent of Syria's influence in Lebanon.

In the hours following the funeral, gunmen fought street battles in Beirut and the northern city of Tripoli. Sectarian clashes killed at least five people, and on Monday cracks of gunfire rang out in Beirut as soldiers and armored personnel carriers with heavy machine guns took up position on major thoroughfares and dismantled roadblocks.

The outburst of violence appeared to be a sign of a nation hurtling toward civil war.

But this is Lebanon, where traditions of social freedoms, factional loyalties and fanaticism are held in a political balance that gives no group full power to force its agenda nationwide. When that balance is disrupted, such as by Friday's assassination, the result is another cycle of violence that the country appears powerless to escape.

It's too early to know if the al-Hassan killing will plunge the country back into war.

But his death does not appear to be having the kind of galvanizing effect seen in 2005, when former Prime Minister Rafik Hariri was killed in a truck bombing along Beirut's waterfront. Hariri's assassination sparked thundering street protests in Lebanon that forced Damascus to withdraw its tens of thousands of troops from the country after three decades.

Al-Hassan's killing, seven years later, comes at a time of deep divisions both inside Lebanon and beyond. Sectarian tensions already were enflamed over the Syrian civil war, the bloodiest and most protracted crisis of the Arab Spring.

Many of Lebanon's Sunni Muslims have backed Syria's mainly Sunni rebels, while Shiite Muslims and the militant group Hezbollah have tended to back Syrian President Bashar Assad, whose tiny Alawite sect is an offshoot of Shiite Islam.

Hezbollah, the most powerful political and military force in Lebanon, is enduring its own troubles. Backed by Iran and Syria, Hezbollah faces the possibility of losing a crucial ally if Syrian rebels manage to topple Assad.

Its reputation as a popular resistance movement already has taken a severe beating for siding with Syria against the anti-Assad uprising even after it supported Arab revolts in Egypt, Tunisia, Libya and Bahrain.

Assad's fall would be a nightmare scenario for Hezbollah. Any new regime led by the country's majority Sunnis would likely be far less friendly to Shiite Hezbollah, or even outright hostile. Iran remains the group's most important patron, but Syria is a crucial supply route. Without it, Hezbollah will struggle to get money and weapons as easily.

Despite all these divisions, there were hopes that Lebanon might ride out the Syrian crisis.

While the Arab Spring turmoil swept the Middle East, it appeared to leapfrog over Lebanon. Lebanon escaped the tumult in part because its weak government produced no dictator to overthrow - not because the population was satisfied.

That same weakness makes the country vulnerable to manipulation by its neighbors.

Many Lebanese blame Damascus for al-Hassan's killing, saying his work was disrupting Syria's power and influence here.

He headed an investigation over the summer that led to the arrest of former Information Minister Michel Samaha, one of Syria's most loyal allies in Lebanon. He also led the inquiry that implicated Syria and Hezbollah in Hariri's assassination.

Michael Azzi, an 18-year-old interior design student in Beirut, said regional conflicts always blow up in Lebanon.

"Lebanon is becoming a country where everyone can throw their trash," Azzi said. "There are some Lebanese who are always ready to burn their country at the orders of foreign countries."