At least 20 people were killed and more than 212 were injured on Thursday when a car bomb went off near a Hezbollah stronghold in southern Beirut's Dahia quarter, a security source in Lebanon said.
While a Sunni Islamist group claimed responsibility for the bombing, Hezbollah and Lebanese officials said it bore the markings of a Zionist attack and served the interests of Israel.
The Lebanese Armed Forces stated that 60-80kgs. of explosive materials were used in the blast. A witness said at least five nearby buildings were damaged and many cars in the area were destroyed. The blast sent a column of black smoke over the densely populated area in the south of the Lebanese capital.
Several minutes after Thursday's blast, live television footage showed fires still burning in the street where the explosion took place. The facades of neighboring residential buildings were also badly damaged.
The attack occurred close to the Sayyed al-Shuhadaa (Martyrs) complex, where Hezbollah leader Sayyed Hassan Nasrallah often addresses his followers.
A witness said that "Hezbollah forces hermetically sealed the area, and dozens of ambulances arrived at the scene."
A Sunni Islamist group calling itself the Brigades of Aisha claimed responsibility for the explosion, saying it targeted Hezbollah and promising more attacks.
"This is the second time that we decide the place of the battle and its timing...And you will see more, God willing," said a masked man, flanked by two others brandishing rifles, in a video statement addressed to Nasrallah.
Sectarian tensions have been high in Lebanon following the intervention of Shi'ite Muslim Hezbollah in support of Assad against a two-year revolt led by Syria's Sunni Muslim majority. Hezbollah also fought a month-long war with Israel in 2006.
Senior Hezbollah figures said that the blast "has Zionist fingerprints all over it."
Vice President of the Higher Shiite Council, Sheikh Abd al-Amir Kabalan, said the the attack "serves the Zionist agenda in the area."
Lebanese President Michel Suleiman also said that the attack bore the hallmarks of "terror and Israel."
Lebanese prime minister designate Tammam Salam warned that "if the situation in Lebanon continues like this, the country will collapse."
He added that "the terror attack in south Beirut is the act of cowards, which serves Israel's interests."
Lebanese Interior Minister Marwan Charbel suggested that the attack may have been Israeli retaliation for explosions that wounded four Israeli soldiers who allegedly infiltrated southern Lebanon last week.
"The terror attack was planned well. It could be connected to the wounding of the Israeli soldiers in al-Labouneh in southern Lebanon," Charbel said.
Nasrallah claimed responsibility for the attack in an interview with Al-Mayadeen television on Wednesday. On Tuesday, Defense Minister Moshe Ya’alon said the incident was isolated and that he did not view it as an escalation.