The Lebanese are on edge. Each bombing, rocket attack, and clash—whether in the north in Tripoli or the east in the Bekaa Valley—reminds them that the big one could be out there, ready to turn their world upside down.

The car bombing Monday in a Beirut suburb, in the heart of a Hezbollah stronghold, wasn’t the big one—fortunately there were no deaths, although more than 50 were wounded—but it is being taken as a warning of what could be impending: an attack that finally triggers full-scale sectarian warfare between Sunni Muslims and Shiites across this small Mediterranean country.

The blast that ripped through the densely populated southern Beirut suburb of Dahyeh has prompted yet more fears that Lebanon risks being dragged back into civil war. The last one stretched for 15 years, left 120,000 dead, and wounded 1 in 4 Lebanese. Since then a fragile balance has been observed, giving all of Lebanon’s main religious sects a share in government power. There has been a relative, shaky peace with occasional alarms—such as the 2005 assassination of Rafik Hariri, the former prime minister, and Hezbollah’s invasion of west Beirut in 2008. Both risked plunging Lebanon back into violence, but in the end total disaster was averted.

Now few Lebanese are confident that another escape can be pulled off. In the past few months, as the drums of violence have beaten, the hotels, bars, and restaurants of Beirut have become emptier. Tourism is down. In swanky nightspots such as the Skybar, the Lebanese rich admit their fears and explain that they are shifting their money overseas and preparing escape options abroad. “They are ruining Lebanon,” says a bejeweled middle-aged divorcée. “But we won’t let them,” she adds before disclosing that a boyfriend is checking out apartments in Paris.

The Syrian civil war that’s inflamed sectarian Muslim divisions across the Middle East has done special harm to Lebanon, bringing to the fore radical Sunni clerics such as Sheik Ahmad al-Assir, who is baying for the blood of apostate Shiites and propelling Hezbollah into an intervention in Syria on behalf of its patron, President Bashar al-Assad.

A couple of politicians, including Parliament Speaker Nabih Berri, a Shiite, sought to blame Israel for the bombing—an easy target in Lebanon, which has seen its fair share over the years of underhanded Israeli maneuvers, black ops, and false-flag assassinations. “The southern suburbs, since the ’80s, have been the target of Israeli-organized crime, terrorism, and sabotage, as well as enemy [attacks] by air and sea that destroyed and killed during the July [2006] war,” he said.

And angry Shiite residents in Dahyeh, surveying the debris, shattered apartment buildings, and burning cars with the cries of the injured ringing in their ears, echoed the hue and cry that Berri and others eagerly have tried to unleash, saying that they too blamed Israel “and those working to serve Israel's interests.”

But few here believe the Israelis are the authors of a blast that was designed to add insult to injury, coming as it did on the eve of the holy month of Ramadan.

Just last week Lebanon’s outspoken interior minister, Marwan Charbel, warned of the possibility of “dangerous security incidents, including assassinations and bombings,” in Lebanon and said Lebanese politicians, both of the Hezbollah-dominated March 8 coalition of parties and their Sunni opponents in the March 14 alliance, were in danger.

And immediately after the blast, Lebanon’s president, Michel Suleiman, dubbed the explosion a “reminder of the black days experienced by the Lebanese in the past,” a reference to the 1975–90 civil war. He urged “understanding and dialogue between the Lebanese” and for a halt to “resorting to such methods in conveying political messages.” He didn’t mention Israel, which hardly needs to foment trouble in Lebanon when the Lebanese are doing a good job of it themselves.

Most view the bombing as retaliation for Hezbollah’s military support of Syria’s President Assad. Several groups have served notice of their intentions to hit Hezbollah, from homegrown Sunni radicals frustrated by Hezbollah’s increasing dominance in Lebanon and furious with Lebanese Shiites for their support of Assad to al Qaeda affiliate Jabhat al-Nusra, which received a drubbing at the hands of Hezbollah in a battle in a Syrian border town.

The Free Syrian Army’s military commander, Gen. Salim Idris, warned recently that Hezbollah’s backing of Syria’s president would be met with retaliation and the targeting of its strongholds in Lebanon. Days after he spoke in May, two rockets were launched from the foothills of the Druze Mountains, targeting the Shiite southern suburbs of Beirut, although they fell short. There have also been episodic rocket attacks on Bekaa Valley Shiite towns fired from Syrian rebel-held positions.

A Lebanese intelligence source hazards that jihadists from al-Nusra are most likely behind the blast, arguing that the group has expertise in car bombings. The operation was well planned and skillfully executed, with the car bomb being maneuvered into a parking lot in the district of Bir al-Abed, inside Hezbollah’s so-called security square, where much of the leadership live and work.

Hezbollah polices the square, cars are frequently pulled over, and strangers in the area can expect to be interrogated and only allowed to proceed when the answers satisfy militiamen. “Not much moves within that square without Hezbollah knowing,” says the Lebanese security source. “Considering Hezbollah’s guard is up at the moment, it was impressive they managed to get that car in.”

Jabhat al-Nusra isn’t alone in possessing those skills. Palestinian and jihadist-aligned fighters in the Palestinian refugee camps in Lebanon are also experienced car bombers, and last month fighters from a refugee camp near Sidon reportedly fought on the side of gunmen loyal to al-Assir in a two-day battle with the Lebanese Army.

But whoever was behind the bombing has certainly added to the tension and foreboding that Lebanon is feeling today.