Angry Sunnis burned tires and blocked roads around Lebanon on Saturday to protest the assassination of a senior Lebanese intelligence official in a bombing widely blamed by the country’s anti-Syrian factions on the government in Damascus.

The assassination brought the violence threatening to engulf the region to the heart of Lebanon’s capital after several years of relative calm, heightening fears that the sectarian tensions already aggravated by the Syrian conflict would erupt into outright war.

Maj. Gen Wissam al-Hassan, who headed the Information Department of the Internal Security Forces, was among at least eight people who died in the mid-afternoon blast on a quiet side street near Sassine Square in the city’s mostly Christian Ashrafiyeh area.

The swift allegations that Syria was responsible stemmed from Hassan’s close association with the Sunni-led anti-Syrian camp in Lebanon and with investigations into bombings and plots that had exposed the role played by Syria’s Lebanese allies, including the militant Shiite Hezbollah movement.

“The one who assassinated Wissam al-Hassan is as clear as the light of day,” Sunni leader Saad Hariri told his Future television network, saying that he held Syrian President Bashar al-Assad responsible for the killing.

(Laris Karklis/The Washington Post)

On Saturday, as the government declared a national day of mourning for the victims of the bombing, Lebanese Prime Minister Najib Mikati voiced support for the view that Syria was responsible, the Associated Press reported.

“I don’t want to prejudge the investigation, but in fact we cannot separate yesterday’s crime from the revelation of the explosions that could have happened,” Mikati said at a news conference after an emergency cabinet meeting.

Lebanon’s rival communites, which fought a bitter and complex civil war from 1975 to 1990, have been polarized by the Syrian conflict, with Sunnis supporting the rebels, Shiites backing the regime and Christians dividing their loyalties between the two sides.

After Friday’s killing, Lebanese braced for the fallout as angry Sunnis, some of them armed, took to the streets in several Sunni areas across Lebanon to protest the killing. Streets in the capital emptied and a brief gun battle was reported in Tripoli between Sunnis and members of the Alawite minority to which Assad belongs.

“There will be repercussions, they will be severe, and I’m afraid the Sunni community will not accept this,” predicted Hilal Khashan, professor of political science at the American University of Beirut.

Syria condemned Friday’s bombing as a “cowardly terrorist attack.’’ But anti-Syrian politicians in Lebanon accused Syria of carrying out the attack to exact revenge against a troublesome rival. They suggested that Syria might also be trying to demonstrate the potential consequences of allowing Assad’s government to fall as it seeks to crush a 19-month-old uprising that has killed about 30,000 people.

The assassination came in a month in which the Syrian conflict has already spilled across the Turkish border, with the two sides trading artillery fire and Turkey dispatching fighter jets to intercept civilian aircraft bound for Damascus.

Hassan was renowned for uncovering Hezbollah’s involvement in the 2005 assassination of Hariri’s father, former prime minister Rafiq al-Hariri, which led to the indictments of four Hezbollah operatives by the United Nations Special Tribunal for Lebanon. Before the bombing, Hassan had served as Rafiq al-Hariri’s personal security adviser.

A 15-foot-deep crater and other scenes of devastation at the site of Friday’s bombing revived memories of the years following Hariri’s assassination, which set in motion a wave of killings that kept the country on edge until Hezbollah seized control of Beirut’s streets in 2008 and went on to secure dominance in the government.

Saad Hariri has lived in Paris since his brief tenure as Lebanon’s prime minister ended last year, but he declared after Friday’s attack that “the Lebanese people will not be silent on this heinous crime’’ and that he would “not remain silent.’’

The White House made no direct mention of Syria in a statement condemning the attack but said that “Lebanon’s security and stability are vital for both the Lebanese people and its neighbors.’’

Most of the anti-Syrian politicians who accused it of carrying out the assassination of Hassan linked the attack to a sting operation in August that exposed a plot by a close ally of Assad’s to mount a bombing campaign against Sunnis allied with Syria’s rebels.

Former information minister Michel Samahah was charged in the plot along with one of Assad’s top security advisers, Gen. Ali Mamluk, after Hassan recruited an informer who recorded Samahah’s conversations outlining the plan to assassinate leading Sunnis in a string of bombings.

“Wissam al-Hassan was a very important man in Lebanese politics, he was an important man in the great divide splitting the country, and he was an important man in the police work that has uncovered many sensitive things,” said Mohammed Chatah, an adviser to Hariri. “One cannot begin to understand this assassination except against that background, and his closeness to the Hariri family.”

“The message sent today by the explosion in Ashrafiyeh is signed by the hand of Bashar al-Assad and his men,” Druze leader Walid Jumblatt told Lebanon’s LBC TV network, identifying the motive as Hassan’s role in exposing the Samahah plot.

In condemining the bombing, Syrian Information Minister Omran al-Zoubi said that “such terrorist acts are condemned and unjustifiable wherever they happen,” according to a statement carried by the official Syrian Arab News Agency, or SANA.

Hezbollah did not apportion blame. A statement by the movement hailed Hassan as a “martyr” and called for a full investigation.

The 1975-90 Lebanese civil war drew Syrian troops into Lebanon — first as peacekeepers, then as participants and occupiers — until the 2005 assassination of Hariri forced them to depart amid widespread allegations that Damascus was responsible for his death.

The latest bombing coincided with mounting evidence that both Hezbollah and the Hariri faction are being drawn more deeply into the Syrian conflict. The recent death of a senior Hezbollah commander while performing what a Hezbollah Web site called “his jihadist duty” caused a stir across Lebanon, seemingly affirming allegations by the Syrian rebels and the U.S. government that Hezbollah is dispatching fighters to aid Assad’s efforts to crush the revolt against his rule.

Meanwhile, numerous press reports have identified Oqab Saqr, a member of parliament from Saad Hariri’s movement, as a major supplier of arms to Syrian rebels. Hariri said in a statement on the eve of the bombing that Saqr had been assigned to act as a special envoy to the Syrians fighting Assad’s rule.

Apart from a few skirmishes, however, the tensions in Lebanon have until now been contained amid many indications that Hezbollah is determined to prevent a crisis that could jeopardize its hold over the country. The collapse of the Syrian government, on which Hezbollah has traditionally relied for political, logistical and military support, would isolate the movement from its chief ally, Iran, and most likely embolden Lebanon’s Sunnis to challenge its control.

A number of recent failed or thwarted assassination attempts targeting anti-Syrian politicians have kept the country on edge, however. In one instance, a sniper’s bullet missed by inches the Christian leader Samir Geagea at his mountaintop home. In another, explosives were discovered in an elevator used by a prominent lawmaker from Hariri’s movement.

Friday’s blast in east Beirut gouged a deep crater and blew cars into pieces that landed blocks away, said George Azzi, who lives nearby and ran outside into crowds of screaming people, smoke and debris. “I’m worried that we’ll return to the events of the past, with random explosions all around town,” he said, expressing widespread concern that the blast may signal the start of a bombing campaign.