Tensions are high in Lebanon, following a general strike and clashes last week that stirred memories of the country's vicious civil war in the 1970s and 80s, and raised fears that a repetition could erupt at any moment.
By Jim Muir
BBC News, Beirut
At least seven people were killed and hundreds injured in the violence.
For many Lebanese, the most worrying confrontation was between Shia and Sunni Muslims, respectively opponents and supporters of the Western-backed Beirut government.
Sectarian violence has claimed thousands of lives in Iraq
Their bloody clashes on the streets of the capital evoked sectarian tensions that are raging elsewhere in the Middle East, notably Iraq.
A few days after the Beirut clashes, and with everybody on tenterhooks fearing that the smallest spark could trigger a conflagration that might engulf the whole country, it was time for the Shias to observe the most significant day in their religious calendar - Ashura.
Hundreds of thousands of them came together in Beirut's southern suburbs, heavily Shia in population, and a Hezbollah stronghold - that is why parts of it were devastated during last summer's Israeli bombings.
Old and young, men and women, babes in arms, almost everybody dressed in black, in mourning for the Imam Hussein, grandson of the Prophet Muhammad.
More than anything else, the martyrdom of Hussein over 13 centuries ago has given Shia Islam the defining characteristics at the heart of its ethos: suffering and sacrifice in the face of oppression, the patience and endurance of the downtrodden, and reverence for the ultimate sacrifice, martyrdom.
But that does not necessarily mean passively accepting death and defeat.
One of the slogans much on display during Ashura here, was: "The Victory of Blood over the Sword".
In other words, we will make our sacrifices, give our martyrs, but we hope in the end to win - as indeed Hezbollah feels it did, last summer, in the war with the Israelis.
In fact, Shia Islam is on the march, throughout the region, whose faultlines - sectarian, ethnic and political - have been perilously exposed by the tectonic pressures currently exerted on it.
When sectarian strife broke out between Sunnis and Shias in Iraq, especially after the attack on the Shia shrine at Samarra a year ago, people began talking of Iraq as "the new Lebanon".
Sectarian revenge killings between Iraqi Shias and Sunnis are now claiming more than 100 lives every day.
If the new American push to bring the situation in Baghdad under control does not work - and there is certainly not unbridled optimism on that score - there are strong fears that Iraq may descend into chaos and fragmentation, in a civil war whose repercussions would likely be felt in many parts of a region where tensions between Sunnis and Shias are already rising.
In Iraq, as in Lebanon, there is a strong feeling among many ordinary people that they are simply pawns, victims of a wider struggle between regional and international powers fighting out their proxy battles over the balance of power.
On one side of that battle, the United States and its strategic ally Israel, with a certain measure of wider Western support; on the other, Iran, and its strategic ally, Syria.
As the battle hots up, so tensions on the ground have broken into divisive violence, in Iraq, in Lebanon - also in the Palestinian territories, though the rifts there are not sectarian but political in nature.
The Islamist movement Hamas, which won last year's elections, is Sunni, as are its opponents in the mainstream Fatah faction.
But Hamas is supported by Shia Iran, as are the Shia movements in Iraq and Lebanon.
After decades of upheavals, it is a home truth to many people in the region, that these are fights which neither side can win.
The US is backing the opponents of extremists - Shia and Sunni alike
Who won 15 years of civil war in Lebanon? Nobody. Everybody lost.
The guiding principle of settlement efforts here has always been "No Victor and No Vanquished".
Movements such as Hezbollah and Hamas, and the Shia and Sunni groups in Iraq, have roots going deep into communities and into history.
Israel is the regional superpower. But it came nowhere near destroying Hezbollah last summer.
But for President George W Bush's America, it is all part of the "war on terror", against those villains from the "Axis of Evil" - Iran and Syria.
Enemies - the extremists - Sunnis and Shias alike - have to be isolated, confronted, and defeated.
So Washington has given millions of dollars to Palestinian Authority President Mahmoud Abbas, the Fatah leader, to help him defeat Hamas; and it was instrumental in winning billions of dollars of aid pledges for the Sunni-led government in Beirut, to help it defeat Hezbollah and stave off Syrian and Iranian pressures.
Thousands more US troops are heading for Iraq, and another naval battle group, to hover menacingly off Iran's coast in the Gulf.
If calming all these conflicts and turmoil needs Washington to reach a strategic entente with Iran and Syria, that seems highly unlikely under George W Bush.
In the meantime, the region remains in grievous danger of exploding out of control, especially in terms of the Sunni-Shia divide.
Despite the fact that it is allied to the United States, Saudi Arabia, which sees itself as the custodian of Sunni Islam, has seen the dangers.
It has been talking intensively to the Iranians, and that dialogue is partly credited with persuading the factions in Lebanon to draw back from the brink.
The Saudis are also brokering a ceasefire between Hamas and Fatah in the Palestinian territories, though it is proving difficult to consolidate.
If the Americans are pulling in different directions, it is hard to see how local and regional initiatives can get very far.
From Our Own Correspondent was broadcast on Saturday, 3 February, 2007 at 1130 GMT on BBC Radio 4. Please check the programme schedules for World Service transmission times.