A powerful car bomb tore through the heart of Beirut's Christian sector Friday, killing a top security official and seven others in a devastating attack that threatened to bring the war in Syria directly to Lebanon's doorstep. The blast sheared the balconies off apartment buildings, upended cars and sent dazed rescue workers carrying bloodied children into the streets.

Dozens of people were wounded in the blast, the worst the Lebanese capital has seen in more than four years. The state-run news agency said the target was Brig. Gen. Wissam al-Hassan, head of the intelligence division of Lebanon's domestic security forces.

Al-Hassan, 47, 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.

"Whenever there is a problem in Syria, they want to bring it to us," said Karin Sabaha Gemayel, a secretary at a law firm a block from the bombing site, where the street was turned into a swath of rubble, twisted metal and charred vehicles.

"But you always hope it will not happen to us. Not again," she said.

Samaha is accused of plotting a campaign of bombings and assassinations in Lebanon at Syria's behest, to spread sectarian violence in Lebanon. Also indicted in the August sweep was one of the highest aides to Syrian President Bashar Assad.

A senior Lebanese police official, speaking anonymously because he was not authorized to talk to the media, said Samaha confessed to having personally transported explosives in his car from Syria to Lebanon with the purpose of killing Lebanese.

Analysts said al-Hassan's killing was a clear signal that Lebanon cannot insulate itself from the Syrian conflict, which has been the most sustained and powerful challenge to the 40-year Assad family dynasty.

"The regime in Damascus will look at his death with much comfort," said Ayham Kamel, a Middle East analyst at the Eurasia Group in London. "One figure, hostile to Syria's interests, is out of the picture."

In Washington, the Obama administration condemned "in the strongest terms" what it called a terrorist attack.

National Security Council spokesman Tommy Vietor said in a statement that there was "no justification for using assassination as a political tool," adding that the U.S. would stand with the Lebanese government in bringing to justice those responsible "for this barbaric attack."

Friday's blast also was a reminder of Lebanon's grim history, when the 1975-1990 civil war made the country notorious for kidnappings, car bombs and political assassinations. Since the war's end, Lebanon has been a proxy battleground for regional conflict, and the Mediterranean seaside capital has been prey to devastating violence shattering periods of calm.

Friday's explosion ripped through a narrow street at midafternoon in Beirut's mainly Christian Achrafieh neighborhood, an area packed with cafes and shops. Doors and windows were shattered for blocks, and several blackened cars appeared to have been catapulted through the air.

Bloodied residents fled their homes while others tried to help the seriously wounded. One little girl, apparently unconscious and bleeding from her head, was carried to an ambulance in the arms of a rescue worker, her white sneakers stained with blood.

Al-Hassan's body was so disfigured in the blast that his bodyguards only recognized him from his sneakers, said a paramedic at the scene.

A Lebanese security official said al-Hassan, who was married with two children, had just returned from visiting family in Paris. He was either on his way to or from work in a non-armored car with his driver, who also was among the dead, said the official, who spoke on condition of anonymity because he was not authorized to give information to the media.

At a nearby hospital, George Hadar was waiting for his 27-year-old daughter to get out of surgery for her wounds — including facial injuries from flying glass and the loss of her eye. His granddaughter, 5-year-old Christa, sat in his lap, her yellow Mickey Mouse shirt covered with blood.

"I hear journalists on the radio talking about body parts and corpses all over the place where my daughter lives," Hadar said. "I drove down here in a daze."

There were immediate fears that Friday's violence could lay bare seething sectarian tensions in Lebanon. The countries share a complex web of political and sectarian ties and rivalries, often causing events on one side of the border to echo on the other.

Many of Lebanon's Sunnis have backed Syria's mainly Sunni rebels, while Shiites have tended to back Assad. Al-Hassan was a Sunni whose stances were widely seen to oppose Syria and the country's most powerful ally in Lebanon, the Shiite militant group Hezbollah.

Soon after the blast erupted, crowds began blocking roads, burning tires and shooting in the air in Sunni areas of Beirut and northern Lebanon. In the eastern Bekaa Valley, angry protesters closed the border crossing that links Lebanon with Syria.

In the northern Lebanese city of Tripoli, pro- and anti-Syrian groups fought with rocket-propelled grenades and automatic rifles. One person was killed, according to security officials. Elsewhere, clashes pitted gunmen in a Sunni neighborhood against those in an Alawite neighborhood of the city. Assad belongs to the tiny Alawite sect, an offshoot of Shiite Islam.

Even as the rubble smoldered in Beirut, Lebanon's fractious political leaders began taking sides. Syria ally Hezbollah condemned the attack and expressed a "state of great shock over this terrible terrorist crime."

But the anti-Syrian blocs placed the blame squarely on Assad.

Former Prime Minister Saad Hariri, a Sunni politician whose powerful father was assassinated in 2005 in a massive truck bombing along the Beirut waterfront, said the Lebanese people must not remain silent about this "heinous crime."

Asked who he blamed, Hariri said: "Bashar Hafez Assad."

Speaking to the Al Arabiya TV station, Walid Jumblatt, leader of the Druse sect, also accused Assad of being behind the killing.

"He is telling us that even though he turned Syria into rubble, 'I am ready to kill in any place'" Jumblatt said.

For much of the past 30 years Lebanese have lived under Syrian military and political domination.

That grip began to slip in 2005, when former Prime Minister Rafik Hariri was assassinated. Syria was widely accused of involvement — something it has always denied — and Damascus was forced to withdraw its troops.

But the killings of anti-Syrian figures continued for several years, and opponents of Assad say he has maintained his influence through proxies in the government.

"The fate of Syria and Lebanon were, are and will always be inextricably linked, for better or worse," said Bilal Saab, a Syria expert at the Monterey Institute of International Studies.

The last major bombing was in 2008, when a car bomb killed a senior Lebanese anti-terror police official who was investigating dozens of other bombings. Four others were killed and 38 wounded in the blast in the Christian Hazmieh neighborhood.

After that, there was relative calm until the uprising against Assad began in March 2011. Since then, there have been sporadic gun battles between pro- and anti-Assad factions, particularly in northern Lebanon.

The explosion shocked a city known for its rollicking nightlife into silence Friday night, as streets that normally would have been packed with cars and partygoers were largely deserted.

"I'm very worried about the country after this explosion," Beirut resident Charbel Khadra said. "I'm worried the explosions will return — and this is just the first one."

"It is a message," said Marwan Rifa, who was working as a legal assistant near the explosion site. "And the message is, you will never live in peace."