By Jim Muir
BBC News, Beirut
The double bomb attack on buses in the Christian mountains north-east of Beirut could not have been more provocative, coming at a time of extreme political tensions that had already taken Lebanon to the brink of civil war.
Many Lebanese believe the intention is to foment civil strife
The bombs exploded just 24 hours before a mass rally planned to take place in the heart of the capital, with anti-Syrian factions urging a huge turnout to mark the second anniversary of the assassination of RafiK Hariri, the former prime minister.
Thousands of their opponents, led by Hezbollah, are already encamped in the immediately adjacent area where they have been physically besieging the main government office since 1 December.
With the potential for a disastrous collision between the two factions all too obvious, there had been widespread calls for restaint on what many hoped would be a national occasion bringing the Lebanese together rather than dividing them.
The double bombing will reinforce the conviction of many that hidden hands are at work trying to drive them apart and foment civil strife.
Unlike the violent sectarian and political street clashes in January that raised memories of the 15 years of civil war in the 1970s and 1980s, the bus explosions were clearly far from spontaneous, but required careful coordination, planning and organisation.
The Bikfaya area where the attack took place is the ancestral home of the Gemayel clan, founders of the Phalangist Party which played a major role in the civil war and is currently firmly in the anti-Syrian camp.
The clan's latest scion, Industry Minister Pierre Gemayel, was murdered by gunmen in a Beirut suburb in November.
This is the first time that bombs were apparently aimed at simply killing and injuring a large number of ordinary people
His father Amin Gemayel, a former president, was among many anti-Syrian leaders who were quick to say that outside hands - implicitly those of Syria - were behind the latest explosions, with the aim of derailing the Wednesday rally.
For the Lebanese, the double bombing also marked a dangerous new development.
There has been a rash of bomb attacks in recent years, including the massive blast that killed Hariri and his entourage in February 2005.
But they have all been directed at specific targets, virtually all of them vocal opponents of Syria.
This is the first time that bombs were apparently aimed at simply killing and injuring a large number of ordinary people, strengthening the impression that whoever was behind them was trying to stir up communal strife in an already explosive situation.
On the brink
The general strike called on 23 January by Hezbollah and its allies in the opposition, and the street clashes two days later, saw Sunnis and Shias battling it out with staves and rocks in Beirut.
Rival pro- and anti-Syrian factions clashed in Christian areas north of the capital.
It is the first time civilians have been targeted with deadly force
The sense that an unstoppable sectarian civil war was only one step away was so strong that leaders on both sides strenously urged their followers to draw back from the brink.
Saudi Arabia, which sees itself as the patron of the Sunnis, who largely back the Fuad Seniora government in Beirut, also coordinated closely with Iran to help reduce tensions.
Tehran is strongly linked to Hezbollah and to Syria, which backs the Lebanese opposition.
With the Arab League Secretary-General Amr Moussa also actively working to defuse the regional and international tensions underlying the crisis, the explosive situation seemed to go on hold, but remains perilously vulnerable to exactly the kind of provocation on the ground staged by the bus bombers.
Anti-Syrian leaders immediately implied their belief that Syria was behind the bombings.
The theory was Damascus wanted to terrorise people into staying away from the Wednesday commemoration rally, as part of a broader campaign to restore its influence and control.
Pro-government forces wanted 14 February to send out a rallying cry
Syrian troops were withdrawn from Lebanon under pressure in the wake of the Hariri assassination two years ago.
With the rally projected to go ahead despite the attacks, Lebanese army and police chiefs are looking at ways at strengthening the already stringent security measures aimed at keeping the two sides from colliding in the city centre during the rally.
Even if the occasion passes off peacefully - as all sides insist it must - the bomb attacks underline the extreme fragility of the situation, and the need for urgent action to defuse the crisis.