Iraqis have already given it a name: the "Bloody Evening". At about 5pm on Saturday 3 February, a Mercedes lorry carrying more than a tonne of explosives was detonated in the Sadriyah neighbourhood of Baghdad, killing 150 people and wounding 300 more. The suicide bomber had driven into a food market in a largely Shia area; the result was the greatest loss of life from a single bomb since the US invasion of 2003.
From weary experience, Iraqis know that it is only a matter of time before Shia militants seek revenge. While hundreds of thousands of Iraqis have sought refuge in neighbouring countries, the majority who cannot leave or cannot afford to leave are trapped in a cycle of sectarian killings that the religious and political leaderships of Shias and Sunnis alike have failed to arrest. Abbas, a Shia friend who left Baghdad recently, told me from his new base in Jordan that he had been forced to go - he had been unable to send his three children to school for fear they would fall victim to the Iraqi sectarian killings that are claiming the lives of a hundred people a day. He described the grisly scene with municipal trucks going out each morning to collect the bodies of those killed the previous night. Corpses found in plastic bags were evidence that the victims had been kidnapped and disposed of when no ransom was paid.
The clash between Sunni and Shia Muslims across the Arab world is already the greatest single cause of strife around the globe. It is taking place within countries and between countries. It has been brewing for years, but only now do governments appreciate the dangers. The hanging of Saddam Hussein in late December took the problem to a new level. Sunnis saw the timing of the execution, on the eve of Eid al-Adha, one of their most significant festivals, as a deliberate insult. Shias worldwide celebrated the death of a man whom they saw as an oppressor. Now the United States and the rest of the western world are attempting, belatedly, to stabilise a situation that they themselves played a major role in creating.
Two years ago, King Abdullah of Jordan warned that a "Shia crescent" was being established across the region. He was referring to the growing influence of Iran in Iraq, Iran's support of Hezbollah in Lebanon, and the strong alliance between Tehran and Syria. The resurgence dates back to the 1979 Iranian revolution, when the religious Shia regime of Ayatollah Khomeini ousted the secular, pro-western shah of Iran. The eight-year Iraq-Iran war could have turned into a Sunni-Shia conflict, particularly as, in the eyes of many, Saddam appeared to be fighting on behalf of all the Sunni regimes in the Gulf. That it did not was because thousands of Iraqi Shias saw it as an Arab-Persian conflict, rather than a sectarian war between Sunnis and Shias in both countries.
Shias constituted the bulk of the Iraqi opposition in exile, and Saddam's downfall ensured that it was only a matter of time before the majority group would seek to regain control. The Sunnis' refusal to accept the change coincided with the arrival of extreme elements associated with al-Qaeda and other Sunni organisations in Iraq. Now, two parallel battles are raging in Iraq: the one of resistance to the American-led occupation, the other a sectarian war.
King Abdullah's prophecy became painfully true last summer for Sunnis in Lebanon. The Israelis' invasion of the south rekindled fears that the militia's large quantities of advanced weapons, donated by Iran to Hezbollah for use against Israel, would in turn be used to strengthen the Hezbollah-Shia influence across Lebanon.
The recent confrontations in Beirut were widely seen as an attempt by the Shia-led Lebanese opposition alliance to bring down the Sunni-led and pro-western government. This explains the scale of violence that Beirut's suburbs experienced. I witnessed scenes similar to those I recall from the Seventies and early Eighties, when the Lebanese civil war was at its height. The difference this time was that it was Muslim fighting Muslim.
The silent majority of Shias and Sunnis in Lebanon are alarmed that their views have been hijacked by respective militias financed and supported by influential governments. King Abdullah bin Abulaziz al-Saud of Saudi Arabia, who has backed the government of the Lebanese Sunni prime minister, Fouad Siniora, sent his national security adviser to Iran to meet the Iranian spiritual leader Ayatollah Khamenei to warn him that the volatile situation in Lebanon threatens to spread into an all-out sectarian war throughout the Arab and Islamic world. The envoy suggested that any attempt by Hezbollah to take over the Lebanese capital would be dealt with in the same way as if the Saudi capital itself had been attacked. The threat had an instant effect, with a call from the Iranian ambassador in Beirut to the leader of Hezbollah to end the confrontation.
The Gulf and beyond
Similar tensions have arisen in the Gulf, especially in Bahrain, albeit on a smaller scale. Jordanian tribes have banned Shias from paying homage at the historical grave site of a prominent Shia imam. The Amman government has recently sought to limit the numbers of Iraqis fleeing across the border into Jordan, fearing clashes between Jordan's Sunni-dominated population and Iraqis seeking refuge in their country.
The spreading conflict between Sunnis and Shias will change priorities. It may, perversely, also divert attention away from historical sources of tension, such as Palestine. Sects and religions that have coexisted peacefully for decades are being dragged into this cycle of violence. The leaderships in Iran and Saudi Arabia are feeling the strain. Iran's role in attempts to convert Sunnis to Shi'ism in Egypt, Syria, Sudan and North Africa has prompted an outcry from King Abdullah bin Abdulaziz. The Saudi monarch has publicly warned Iran about these activities and declared that, whatever Iran's intentions, the Arab world will always enjoy a Sunni majority. Saudi Arabia's foreign minister, Prince Saud al-Faisal, has been more outspoken, calling on Tehran to stop interfering and urging it to "become part of the solution, not part of the problems of our world".
And yet, for a number of reasons, Iran may be taking stock. It is increasingly concerned about the future of Shia minorities in the Gulf region, especially those in Saudi Arabia and Kuwait. There is a growing view in Tehran that Iran has more to lose than to gain from such clashes.
Iran is trying to improve its relationship with the Gulf states, especially Saudi Arabia, partly out of fear of American intentions. A planned UN embargo appears to be prompting Tehran to show a little more flexibility in its dealings with the outside world on the nuclear issue. The Iranians do not want to forfeit vital cards they have to play, further increasing their isolation in a region dominated by Sunnis. This is where the Sunni-Shia dispute comes in, and where the various conflicts interconnect.
The Hamas movement in Palestine would be forced to review its relationship with Tehran if Iran continues its clear support of the Shia-led alliance in Iraq. So would the Muslim Brotherhood in Jordan. Certain prominent voices within these groups have called on Iran to prevent its allies from ghettoising Iraq. During last summer's war in Lebanon, Hezbollah initially enjoyed the support of the main Sunni religious organisations in the Arab world. But this support started to crumble.
The American U-turn
America's botched reconstruction of Iraq attests to a broader failure to understand the root causes and consequences of the growing Shia-Sunni conflict. Following the events of 11 September 2001, the US and several of its allies believed that Sunni countries in the Middle East and the Gulf region were not capable of confronting extremism represented by organisations such as al-Qaeda and its affiliates. They concluded that it was better to forge alliances with the Shias in the region. As George W Bush developed his plans to attack Iraq and topple Saddam, ipso facto this approach hardened.
One of the many unforeseen consequences of the war was the extent to which the Americans were taken by surprise at the scale of influence Iran has on its Shia Iraqi allies. It was only last year that the White House began to take steps to counter-balance this by inviting the Sunnis to the political process. As evidence suggested that Iraqi government forces and Shia-led security organisations were terrorising the population, so the Americans performed a spectacular U-turn. De-Ba'athification - the policy of disbanding the army and all groups that had served under Saddam, which in turn led to a large number of Sunnis swelling the ranks of the various insurgent groups in Iraq - was abandoned. Ba'athists were encouraged to return to their jobs and senior Sunni generals were urged to rejoin the army or claim pensions or compensation for being denied their rights since the fall of the regime.
The role of Iran, both in Iraq and Lebanon, has led Washington to rely once more on its Sunni allies Saudi Arabia, Egypt and Jordan. Washington sees both Syria and Iran playing a double game in Iraq. On the one hand they support the Sunni insurgents militarily, allowing supplies of men and weapons to pass across their borders with Iraq to fight coalition forces. On the other, they provide political support to the Shias to ensure they remain in power.
Washington is also seeking to have it both ways. It is keen to see Iran and Syria co-operating to bring stability and balance to Iraq. Yet it is also trying to prevent both countries from meddling further in Lebanon.
All the while, as alliances of convenience are forged, and as the big powers play out their ambitions in different parts of the region, hostilities between Sunnis and Shias grow. The Middle East is heading for a period of sectarian and civil war. It will not be the only loser.
Pop: 3.8 million
Sunni: 23% (estimate)
Heavily influenced by Syria and a battleground for proxy conflicts between Iran and Israel. Demands of Hezbollah, a Shia political party and militia, have created a stand-off with the Sunni-led government of Fouad Siniora. Clashes between the opposition (backed by Iran and Syria) and government (backed by Saudi Arabia and the US) could lead to civil war.
Key player: Hasan Nasrallah, Shia cleric, leader of Hezbollah. A cult figure in the Arab world, he is demanding early elections to capitalise on popularity after last year’s war with Israel
Occupied Palestinian Territories
Pop: 2.8 million
Shia: less than 1%
Source of anti-Israeli, anti-US Arab sentiment. Failure to form unity government has led to fighting between Sunni Islamic Hamas and secular Fatah, prompting fears of civil war in Gaza. Violence is not sectarian: Iran bankrolls Hamas, while the US supports the Fatah leader and president, Mahmoud Abbas.
Key player: Khaled Meshaal, supreme leader of Hamas. Living in exile in Damascus, he is key to negotiating a unified government
and ending infighting
Pop: 24 million
World’s leading Sunni state and Iran’s opposite number in Sunni-Shia divide. Keen to curb Iranian ambitions in Middle East. Domestic Shia minority, concentrated in oil-rich Eastern Province, has suffered repression, but Shia ascendancy in Iraq has given Saudi Shias new confidence.
Key player: Abdullah bin Saud, king. Launched “national dialogue” between Saudi Sunnis and Shias, but remains opponent of Iran and Iranian-sponsored militias
Pop: 27 million
Sunni-Shia civil war is intensifying. Shias, repressed under rule of Saddam Hussein, are now settling scores. Iran supports
Shia dominance and is using insurgents to undermine the US. Shia-on-Shia violence and a parallel war being fought by both Sunnis and Shias against coalition forces complicate the conflict.
Key player: Moqtada al-Sadr, leader of the Mahdi army. Charismatic cleric with close links to Iraqi government, he controls the country’s most powerful militia
Pop: 70 million
World centre of Shi’ism and only Shia-majority, Shia-ruled state. Feared by US and moderate Sunni Arab states. Maintains regional influence through cash donations, military training and alliances, including Hezbollah (Lebanon), Shia militias (Iraq), Hamas (Palestinian Territories) and the Syrian government.
Key player: Ayatollah Ali Khamenei, Supreme Leader. Shia Islam’s top cleric and highest authority in Iran, Khamenei supports a hardline religious path
Pop: 19.5 million
Ruled by Alawite minority (offshoot of Shia Islam seen as heretical by most Shias), but fragmented religious make-up means it is governed as a secular
state. Political isolation has pushed Syria into anti-western, anti-Israeli alliance with Tehran: it supports Hezbollah against Israel and against the Sunni-led Lebanese government.
Key player: Bashar al-Assad, president. The young leader is keen to draw on Hezbollah’s popularity and Iran’s financial and political clout
Research by Sam Alexandroni and Lucy Knight