BEIRUT — A powerful car bomb exploded in a Hezbollah stronghold in the southern suburbs of Beirut on Tuesday, wounding at least 53 people in the most troubling sign yet that Syria's civil war is beginning to consume its smaller neighbor.
The blast in the heart of the Shiite militant group's bastion of support raised the worrying specter of Lebanon being pulled into the violent Sunni-Shiite struggle in the region, with sectarian killings similar to those plaguing Syria and Iraq.
The Syrian conflict, now in its third year, is whipping up sectarian fervor. Sunni-Shiite tensions have risen sharply, particularly since Hezbollah raised its profile by openly fighting alongside President Bashar Assad's forces. Lebanese Sunnis support the rebels fighting to topple Assad.
While there was no immediate claim of responsibility, there have been growing fears in Lebanon that Hezbollah could face retaliation for its now overt role fighting alongside Assad's troops. The group's fighters played a key role in a recent regime victory to retake control of the strategic town of Qusair, near the Lebanese border, where rebels held sway for more than a year. Syrian activists say Hezbollah fighters are now aiding a regime offensive in the besieged city of Homs.
Syria-based rebels and militant Islamist groups have threatened to target Hezbollah strongholds in Lebanon in retaliation.
The U.N. Security Council strongly condemned the terrorist attack, underlined the need to bring the perpetrators to justice, and appealed to the Lebanese people "to preserve national unity in the face of attempts to undermine the country's stability."
The car bomb struck a bustling commercial and residential neighborhood in Beir el-Abed, an area of particularly strong Hezbollah support, as many Lebanese Shiites began observing the holy month of Ramadan. The blast went off in a parking lot near the Islamic Coop, a supermarket usually packed with shoppers.
"The explosion was so strong I thought it was an Israeli air raid," said Mohammad al-Zein, who lives near the blast site. "My wife was sleeping in bed and all the glass fell on her, injuring her in the mouth, arms and legs."
Beir el-Abed is only few hundred yards (meters) from what is known as Hezbollah's "security square," where many of the party's officials live and have offices. It was heavily bombed by Israeli warplanes during the monthlong war between Israel and Hezbollah in 2006.
The area, where Hezbollah leader Hassan Nasrallah once received dignitaries before the 2006 war, was completely destroyed by Israeli airstrikes. He has since gone underground, only rarely appearing in public and never for more than few minutes, fearing Israeli assassination.
Tuesday's attack inflamed long-simmering tensions in Lebanon, where deadly clashes between Shiites and Sunnis have grown increasingly common as the civil war in Syria has taken on ever darker sectarian overtones. Some Sunnis in Lebanon, many of whom support Syria's rebels, have expressed resentment over what they see as Hezbollah's unchecked power in the country.
The anger was clear among residents of Dahyeh, Hezbollah's stronghold in Beirut's southern suburbs. At the scene of the explosion, some cursed Sunni politicians and Syrian rebels, calling them Israeli agents.
With smoke still hanging in the air, about 100 outraged Hezbollah supporters stormed through the area, carrying posters of Nasrallah and chanting sectarian slogans.
"Shiite blood is boiling!" they shouted as dozens of Hezbollah operatives wearing red caps and holding radios kept watch.
At one point, the Hezbollah agents fired in the air to disperse protesters pelting the interior minister with stones after he inspected the scene of the blast, trapping him for 45 minutes in a building before he was escorted through a backdoor.
Interior Minister Marwan Charbel is seen by some Shiites as sympathetic to hard-line Sunni cleric Ahmad al-Assir, who has agitated against Hezbollah for months and is now on the run.
Clashes between al-Assir's supporters and Lebanese army troops last month in the coastal city of Sidon further increased sectarian tensions in the country.
"We, the sons of Imam Hussein, have been targeted for 1,400 years," said Abbas Kobeissi, a 32-year-old barber being treated for head wounds from flying glass after Tuesday's blast. He referred to the grandson of Islam's Prophet Muhammad, a key figure in Shiite Islam whose death in the 7th century increased divisions between Sunnis and Shiites.
"History is repeating itself," Kobeissi added. "This is a message to Dahyeh. They (Hezbollah) think this will make people rise against the resistance."
Tuesday's explosion was one of the biggest in the capital's southern suburbs since the end of Lebanon's 15-year civil war in 1990, and a major breach of a tightly controlled, high security area.
"It is a large area, heavily populated. No force in the world can protect every area and every street," Hezbollah lawmaker Ali Moqdad said.
The breach raised questions about the group's ability to control the anger it helped unleash through its involvement in the Syrian civil war. At the same time, Lebanese Sunni groups have also joined the fight alongside Syria's rebels, offering logistic and other support.
"Both sides, Hezbollah and Sunni fighters, are directly involved in the Syrian conflict and it's becoming increasingly clear that it's impossible to keep the fighting there away from Lebanon," said Ayham Kamel, a Middle East analyst at the Eurasia Group in London.
"The Syrian conflict has put Hezbollah in a tough spot, with limited choices for its leader Hassan Nasrallah to pursue," he said. "There is a regional Sunni-Shiite confrontation going on in Syria and that puts pressure on all parties in Lebanon, including Hezbollah."
Syria's civil war is increasingly being fought along sectarian lines, with Sunnis dominating the rebel ranks fighting Assad's regime, which is composed mostly of Alawites, an offshoot of Shiite Islam. The fighting has threatened the stability of Syria's neighbors – including Iraq, where a recent surge in car bombings have targeted Shiite areas.
Health Minister Ali Hassan Khalil said 53 people were wounded in Tuesday's blast, which shattered windows and damaged several buildings in the busy area. A security official said the bomb was placed in a car and weighed 35 kilograms (70 pounds).
At least one Syria-based Islamist brigade claimed responsibility for the attack on its Facebook page, but its authenticity could not be verified. The Syrian National Coalition, the main Western-backed Syrian opposition group, denounced "in the strongest terms the terrorist explosion."
"Targeting civilians is a criminal act that goes against the aims of the (Syrian) revolution and its principles," it said in a statement.
Hezbollah lawmaker Ali Ammar blamed "Israel and its tools in the region" for the attack. Hezbollah, like the Syrian regime, refers to those fighting to topple Assad as agents of Israel and the U.S.
The European Union condemned the Beirut bombing, calling it an "appalling act of violence (that) underlines the need for all Lebanese to maintain their national unity."
Television footage from the scene revived memories of the 1975-90 Lebanese civil war when car bombs set by sectarian groups were common. There have been numerous car bombs targeting politicians and journalists since then, but random car bombings have been rare.
In May, two rockets struck the Hezbollah stronghold, wounding four people hours after Nasrallah vowed in a speech to help propel Assad to victory. In June, a rocket slammed into the same area, causing no casualties.
"A further destabilization of Lebanon's security is now very likely," said Charles Lister, an analyst at IHS Jane's Terrorism and Insurgency Center.
"Another line has been crossed," he said, "but the result will likely be a further hardening of the stances held by Hezbollah and its increasingly confident Sunni militant adversaries."
Associated Press writer Barbara Surk contributed to this report.