By Jim Muir
BBC News, Beirut
The latest bomb attack in Lebanon, apparently aimed at an American embassy vehicle, is slightly out of pattern with the many other explosions which have rocked the country over the past three years.
Four people were killed in the bomb blast and 16 wounded
Many of those were meticulously planned and executed operations resulting in the assassination of prominent figures - MPs, journalists and others - who had been vocal in their criticism of neighbouring Syria.
Others were random bombings clearly aimed at spreading fear, destabilising the country and undermining its economy.
Supporters of the Western-backed Beirut government have loudly accused Syria of being behind both kinds of attack - a charge Damascus has repeatedly denied.
They have already categorised this latest explosion as part of the same campaign, despite its unusual target.
It was the first time American targets had been attacked since the 1980s, when the US embassy and marine barracks were blown up and a TWA airliner hijacked.
Sunni Islamic radicals have issued recent threats against American interests in Lebanon and the region. The attack coincided with President George Bush's current visit.
In contrast to many of the earlier bombings, this one appeared to be relatively clumsy.
The powerful explosion shook the mainly Christian Doura area
It missed the target vehicle - which in any case was not carrying any diplomats or American officials.
By chance, an American civilian who happened to be nearby was among those wounded.
Many of the previous attacks had apparently involved much more sophisticated intelligence and operational capabilities.
But Syria's opponents in Lebanon will nonetheless be convinced that, despite the differences, this latest outrage also falls into the general pattern of efforts by Damascus to destabilise its neighbour and resist US influence here.
It came on the eve of a second attempt by the Arab League Secretary General, Amr Musa, to promote a peace plan agreed by Arab foreign ministers in Cairo earlier this month.
Lebanon is currently without a president and in the grip of an acute political crisis caused by deadlock between the Syrian-backed opposition, headed by Hezbollah, and the government.
The factions agree that the next president should be the current Army commander, Gen Michel Suleiman.
But the opposition wants his election to be part of an agreed package deal resolving all outstanding issues, especially the composition of a national unity government in which it is demanding a share big enough to allow it to block decisions it does not like.
There is little optimism that Mr Musa's latest visit will produce a breakthrough.
Newspapers here have predicted the crisis could drag on for weeks, with the latest attack underlining the dangers of further violence.