Former Lebanese Finance Minister Mohamad Chatah was killed Friday in an explosion that rocked a central business district in Beirut.
At least four others were killed and at least 70 were wounded, sources said.
Known for his criticism of Syrian President Bashar Assad, Chatah, 62, a Sunni Muslim, was also a critic of Lebanon's Shi'ite Hezbollah movement and an advisor to former prime ministers Saad Hariri and Rafik Hariri.
Sources at the explosion site said Chatah was on his way to attend a meeting when the explosion occurred.
His killing occurred three weeks before the long-delayed opening of a trial of five Hezbollah suspects indicted for the February 2005 bombing which killed Rafik Hariri, Saad's father, and 21 other people.
Hezbollah has denied involvement in the 2005 attack. Preliminary UN investigations implicated Syrian officials.
Following Friday's attack, Hariri implicitly accused Hezbollah of killing Chatah. "As far as we are concerned, the suspects ... are those who are fleeing international justice and refusing to represent themselves before the international tribunal," Hariri said, referring to five Hezbollah suspects indicted for the 2005 killing of his father.
The explosion was caused by a car bomb and coincided with a meeting of anti-Syrian politicians, according to media reports.
The blast occurred a few hundred meters from the government headquarters and parliament building, near the Starco Center in downtown Beirut. This area is near that where Rafiq Hariri's convoy was struck in 2005.
The army cordoned off the area to prevent people from getting close to the scene, where the twisted wreckage of several cars was still smoldering. The explosion appeared to be the result of the car bomb, but security officials said they had no immediate confirmation.
A tweet posted on his Twitter account less than an hour before the blast accused Hezbollah of trying to take control of the country:
"#Hezbollah is pressing hard to be granted similar powers in security & foreign policy matters that Syria exercised in Lebanon for 15 yrs," the tweet read.
Lebanon has seen a wave of bombings over the past months as sectarian tensions rise over the conflict in neighboring Syria. Hezbollah has sent fighters to Syria to fight alongside Assad, who comes from the Alawite sect, a heterodox offshoot of Shi'ite Islam.
Sources at the explosion site said Chatah was on his way to attend a meeting at Hariri's headquarters when the explosion tore through his car. Hariri himself has stayed away from Lebanon for more than two years, fearing for his safety.
A Reuters witness at the scene said his car was "totally destroyed, it is a wreck." Chatah's identity card, torn and charred, was found inside his car.
Iran, which backs Hezbollah, came under attack in Beirut last month. On November 19, two suicide bombings rocked the embassy compound in Lebanon, killing at least 25 people including an Iranian cultural attaché and hurling bodies and burning wreckage across a debris-strewn street
A Lebanon-based Al Qaida-linked group, the Abdullah Azzam Brigades, claimed responsibility and threatened further attacks unless Iran withdraws forces from Syria, where they have backed Assad's two-and-a-half-year-old war against rebels.
The sound of Friday's blast was heard across the city at around 9:40 A.M. (0740 GMT) and a plume of black smoke was seen rising in the downtown business and hotel district. It shattered glass in nearby apartment blocks and damaged restaurants, coffee shops and offices in the chic district of downtown Beirut.
"I heard a huge explosion and saw a ball of fire and palls of black smoke. We run out of our offices to the streets," said Hassan Akkawi, who works in a finance company nearby.
"The explosion caught motorists driving in the morning rush hour here. There was terror and panic among residents. There was a big ball of fire and panic everywhere and then we learned that Chatah was the target," said Adel-Raouf Kneio.
#Hezbollah is pressing hard to be granted similar powers in security & foreign policy matters that Syria exercised in Lebanon for 15 yrs.— Mohamad B Chatah (@mohamad_chatah) December 27, 2013
Minutes after the blast, ambulances were seen taking victims from the area. A restaurant and a coffee shop were destroyed in the blast, and several cars were on fire, the witness said. There was glass everywhere and the acrid smell of explosives filled the air.
Much of Beirut went into lockdown following the explosion, with police blocking off roads across the city.
After a series of explosions in the capital and in the northern city of Tripoli, the Lebanese army had stepped up security measures ahead of Christmas and New Year, fearing further attacks.
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