The attack has been condemned by leaders in the Middle East, Europe, and the United States. The United Nations Security Council, which last year passed a resolution demanding that Syrian troops leave Lebanon, is due to meet later today to discuss the situation following Hariri's death.
A claim by a previously unknown militant group that it had killed Hariri in a suicide operation because of his ties to Saudi Arabia could not be independently confirmed. Lebanese forces raided the house of a man who appeared in a video claiming responsibility for the attack, but he was not there.
Syria has some 14,000 troops in Lebanon, and has denied playing any role in the death. But U.S. officials seemed to imply Syrian involvement with their comments. White House spokesman Scott McClellan said the killing is "a terrible reminder that the Lebanese people must be able to pursue their aspirations and determine their own political future free from violence and intimidation and free from Syrian occupation."
Whoever is responsible has ushered in a new instability in Lebanon in the run-up to parliamentary elections in May, according to Michael Glackin, the managing editor of "The Daily Star," an English language newspaper in Beirut.
"Certainly, [Hariri's death] has created a massive vacuum in Lebanese politics because he was internationally well known, internationally respected as somebody who was a billionaire and as a politician," Glackin said.
Glackin points out that in his first two terms as prime minister during the 1990s, Hariri had once cooperated with Syria, which has had great influence over Lebanon's internal politics since the end of the civil war.
But more recently, Glackin says, Hariri has called for Syria to withdraw its forces and end its involvement in Lebanese affairs.
Murhaf Jouejati agrees that Hariri's death leaves a political vacuum. Jouejati is a senior analyst at the Middle East Institute, a private policy research center in Washington. He says that in Hariri's absence, there can only be more unrest in Lebanon.
"I believe in the next few weeks we may see some more of this type of thing. There is a lot of tension in Lebanon, and that tension has escalated into harsh rhetoric by either side -- the opposition or the government -- and these escalations have let to this [bombing]. So I think the days ahead for Lebanon are going to be difficult ones," Jouejati said.
Jouejati says the bombing sends a very bleak message to everyone in Lebanon, not just Hariri's political allies.
"I think all of the Lebanese should fear, not only those who have lost their representative, Rafik al-Hariri. The message is: Either someone internally, domestically in Lebanon, or internationally wants to destabilize Lebanon to make the situation more complicated. And so this is the time, really, when the Lebanese really have to be united in the face of an obviously adverse situation to them," Jouejati said.
Asked who benefits from removing Hariri from the political scene, Jouejati responds that there is a long list of people wanting to disrupt Lebanon's democracy. He points out that a Druze rival of Hariri recently escaped assassination.
Jouejati says there are now many who vehemently oppose Hariri, and there are just as many who vehemently oppose Syria's military presence in Lebanon.
But yesterday's bombing probably does not foreshadow a resumption of Lebanon's civil war, according to Nathan Brown, who specializes in Middle Eastern politics at the Carnegie Endowment for International Peace, another Washington think tank.
Brown tells RFE/RL that the past 15 years of relative quiet have not been merely an extended cease-fire.
"There's a very changed cast of characters from 30 years ago. On top of that, there are different issues. [The] Palestinian issue was an issue then. It's much less of one now, certainly not in the same way. The Syrian presence [in Lebanon] itself was an effect of the earlier civil war. Now, if anything, it's very much at issue," Brown said.
Brown points out that one catalyst for the civil war that began in the 1970s was the presence of huge Palestinian refugee camps in southern Lebanon, and Israel's invasion to confront militants operating from those camps.
Now, Brown said, the chief political debate in Lebanon concerns Syria's political influence, and the presence of its troops. This debate has intensified in recent months after the United Nations Security Council passed a resolution calling for their withdrawal.
"Over the last year or so, there's been an increasingly open debate in Lebanon about the Syrian presence in a way that the country hasn't seen for a long time. That is a heated debate, it's [a] very, very sensitive debate, but we don't seem to be at the point at which that debate would erupt into total civil war," Brown said.
In part, Brown said, it has been Syria's involvement in its neighbor's politics -- and the presence of Syrian troops there -- that have contributed to Lebanon's stability over the past 15 years. Whether Syria can still keep the peace after Hariri's death, he said, is anyone's guess.