It is the sixth blast to hit Beirut
and the surrounding area in the past four weeks. Two people have been killed in the five previous explosions, all caused by bombs.
Hashem Ahelbarra, Al Jazeera's correspondent at the scene, said: "This is going to be a signal to the Lebanese that those who are carrying out the explosions are tracking people with real intelligence capability and manpower.
"Those who wanted to target [Eido] would have followed him from A to Z and when they saw him leave his car they would have detonated the bomb.
|Walid Eido [AFP]|
"Most Lebanese newspapers often described Eido as a staunch opponent of the Syrians and a strong ally of Saad al-Hariri."
Al-Hariri is the son of Rafiq al-Hariri, a former prime minister, who was assassinated in Beirut in February 2005. He now leads the Future movement.
Walid Eido, who was in his 60s, was a Sunni Muslim member of Hariri's Lebanese Future Movement, which is part of the March 14 majority bloc.
Eido was a retired judge, who had been critical of Hezbollah and Emile Lahoud, the president, who recently called on Fouad Siniora, the prime minister, to launch an investigation into last year's war.
The explosion occurred less than two kilometres from the site of the suicide truck bombing that killed al-Hariri. Twenty-two other people died in that blast.