Lebanon's prime minister vowed to find the assassins after a 35 kg bomb killed yet another anti-Syrian member of parliament and six others in an area east of Beirut.
The explosion on Wednesday killed Christian Phalangist party legislator Antoine Ghanem, two of his bodyguards, and four others passing by the area.
Ghanem was the latest of at least eight such political figures targeted during two years of political turmoil of Lebanon, the scene of a power struggle among Christian political parties, Hezbollah Shia parliamentarians and militia, Sunni Islamists and Syrian proxy groups. Journalists have also been killed in such attacks.
Hospital sources said 56 people were treated as a result of Wednesday's explosion, and around 30 stayed there for treatment.
Lebanese Premier Fouad Seniora denounced the assassination and vowed that the culprits would be brought to justice.
"The assassination of Antoine Ghanem is a clear message to silence the voices of freedom," Seniora said in a written statement. "I vow that the hands of assassins will not escape punishment."
Initial investigations showed the killing was done by a 35 kg bomb detonated by a remote-control device, a Lebanese security source told DPA.
The bomb attack came less than a week before presidential elections slated for Tuesday.
In 2004, the term of the incumbent, Emile Lahoud, was extended for three years, a move backed by Syria that helped provoke massive international pressure for Syria's withdrawal from the affairs of the Middle Eastern country.
Anti-Syrian legislator Antoine Zahra said the killing aimed "to reduce the number of anti-Syrian deputies in the parliament and to block the presidential elections".
Ghanem's death has reduced the anti-Syrian majority to 68 in the 128-member parliament.
At the Lebanese-Canadian hospital where the bodies were taken, family and relatives mourned the dead legislator.
Ghanem's widow was seen being whisked inside the hospital along with relatives and key members of the Phalangist party.
Black smoke billowed from the blast area between Horesh Tabet and the Christian neighbourhood of Sin el Fil. Several cars were set ablaze. The area is close to the office of former deputy and presidential candidate Nassib Lahoud, a cousin of the current president but on the opposite side of the political fence.
The area is also home to former President Amin Gemayel, head of the Phalangist party, whose son, Industry Minister Pierre Gemayel, was assassinated last November.
A Red Cross volunteer at the scene said the legislator was still breathing when they reached the area but died while in ambulance on the way to the hospital.
"The assassins are the Syrians and they want to kill all of us," shouted a woman as a shocked crowd was kept at bay by a police cordon at the scene. The daughter of the woman, who refused to identify herself, was wounded and taken to hospital.
"We were at home when we felt that an earthquake had hit our area and shattered rubble fell on our heads," she added.
Nearby buildings were heavily damaged and broken glass littered the street near the Librairie Antoine, a famous bookstore.
The last victim of such bomb attacks was Walid Eido three months ago, another anti-Syrian MP who died along with nine other people, including his son and two bodyguards.
The series of assassinations began in February 2005 when former prime minister Rafik Hariri became the first - and most prominent - anti-Syrian political figure to be killed in a bombing.
The mass protests that followed eventually resulted in Syria withdrawing its forces from Lebanon.
In Washington, the US condemned Wednesday's attack and said the murder represented a pattern of such acts against anti-Syrian politicians "designed to intimidate those working courageously toward a sovereign and democratic Lebanon".
White House spokeswoman Dana Perino however said she was "not prepared to assign blame to anybody at this point".
King Abdullah II of Jordan called the assassination "an ugly crime that targets Lebanon's stability and security".