Is this man the mastermind of the massacres?

The devastating effects of the slaughter on the holiest day of the Shia Muslim calendar were there for the world to see. But who is behind the attacks? The Americans are pointing the finger at Abu Musab al-Zarqawi, a Jordanian militant with links to al-Qa'ida. But Justin Huggler, who witnessed the carnage in Karbala first hand, says the evidence on the ground is far from conclusive

I found myself in the middle of a massacre. All around me, people were dying as suicide bombers detonated their explosives and mortars fell in the middle of vast crowds. The survivors were spattered with the blood and skin of the dead. Ashoura, the holiest day of the Shia Muslim calendar, had been turned into slaughter at their holiest shrines.

I found myself in the middle of a massacre. All around me, people were dying as suicide bombers detonated their explosives and mortars fell in the middle of vast crowds. The survivors were spattered with the blood and skin of the dead. Ashoura, the holiest day of the Shia Muslim calendar, had been turned into slaughter at their holiest shrines.

My companions, Haidar and Mohammed, and I desperately tried to find our way out of the maze of narrow back streets in Karbala, not knowing whether we were rushing into the path of the next explosion. And they kept coming: I counted nine of them in all. It is hard to grasp the scale of what happened around us.

In Baghdad at the same time the climax of the religious celebration was being shattered by a series of explosions. As many as 185 people may have died in the two cities, with more than 400 wounded, in Tuesday's attacks.

It was a desecration of all that is holiest to the Shia. Karbala was a massacre, and women and children were among the victims. Whoever was behind it had them penned into a terrible trap. Even as they fled the first explosion, they were rushing unsuspecting into the path of the next. And as the survivors turned and fled from that, they were hit by another.

It left the streets of Karbala swimming in blood. The Arabic news channels broadcast what are probably some of the most graphic television pictures of wide-scale carnage ever shown - apart, of course, from the 11 September World Trade Center attacks.

Yet for all that the monstrous scale of it was shocking, the fact that it happened didn't come as a surprise at all. There was something terribly predictable about that first explosion we heard from 100 metres away. What may have saved our lives is the fact that we had left the crowded main streets just minutes before it happened. The crowds were too easy a target for a suicide bomber, we decided. Slightly embarrassed that we might be being paranoid, we cut down a back street. And then the first explosion came. It was not paranoia.

Everybody feared something like this was going to happen. There were dire warnings, and talk of massive security from the Americans - though in fact, on the day, the security was woefully inadequate. We were debating whether to risk being on the streets at all. That over a million Shia still came to Karbala in those circumstances may seem surprising. But as we fled the city, we saw them still streaming in in their hundreds of thousands.

We stopped some and asked them: hadn't they heard? Heard that there had been nine massive explosions in the middle of the crowds inside the city? That many inside were dead, or dying, and no one knew if the attack was over yet? No, they said, they had not heard. But they didn't turn back.

"We trust in God," they said, and continued heading into the city, into that nightmare we had just escaped, and were still shaking from. That is an insight into the emotional significance of the Ashoura ceremony, long banned under Saddam, to the Shia - and an insight into how tough Iraqis are.

However expected it was, there are a lot of questions still to be answered about what happened in Karbala that day. Iraqi police appeared to have worked out how much of it was done. How the first explosion was a suicide bomber who just mingled with the crowd. How those responsible appear to have smuggled explosives into the city on the wooden carts that are used to bring in food supplies and carry elderly and crippled pilgrims during Ashoura, and how some of the explosions were probably mortars fired into the crowd from outside the city.

But, despite the confidence with which American military spokesmen appeared before the cameras within hours to pin the blame on Abu Musab al-Zarqawi - a Jordanian militant linked to al-Qa'ida whom the US accuses of being behind many of the suicide bombings and other outrages in Iraq - we still have remarkably little hard evidence as to who was really behind the simultaneous attacks in Karbala, and on a Shia shrine in Baghdad on Tuesday.

As for why it happened, the American answer was simple: it was to foment a civil war between Iraq's Shia majority, long repressed under Saddam, and the Sunni minority, who now fear they are losing their grip on power.

The whole sequence of events seemed to follow the American script almost too perfectly. Only last month, the US leaked to The New York Times what it claimed was a letter from Zarqawi to al-Qa'ida leaders in Afghanistan, intercepted on a computer disk militants were trying to smuggle out of Iraq. In that letter, he asked for help setting up spectacular attacks against Iraqi Shia in order to provoke reprisal attacks against the Sunni. The plan, as spelled out in the letter, was for the violence to spiral into a civil war.

Zarqawi may well have been responsible for what happened last week: he is as good a candidate as anyone else. But even in the US there is scepticism, with one well-placed official seeing his alleged letter to al-Qa'ida as more of an empty boast, or a plea for recognition, than a plan of action. Others add that it would be impossible for foreign militants to move into such a closed society as Iraq, where people are deeply suspicious of outsiders, including non-Iraqi Arabs, and carry out a campaign of violence without significant Iraqi participation at every turn.

The commander of US forces in the Middle East, General John Abizaid, has told a US congressional committee that American forces have evidence Zarqawi was behind the attacks, but none of it has been made public. And the US occupation forces are no longer considered a trustworthy source by most in Iraq. It was an American military spokesman who, on the day General Abizaid was nearly killed in a carefully planned ambush in Fallujah, claimed that "95 per cent of the population in Fallujah support the coalition" - a laughable description of the city that has come to symbolise the Iraqi resistance.

And the waters have been muddied further by what appeared to be a rare denial from al-Qa'ida, emailed to the London-based Arabic newspaper Al-Quds al-Arabi, and a statement signed by several Iraqi resistance groups the next day, claiming that Zarqawi was killed in American bombing last April. The letter the Americans claimed to have intercepted was a fake, the statement alleged.

That may all be calculated disinformation, and the American claims about Zarqawi may be true. But, unless the Americans do have some proof they are withholding from the public, it is by no means an open-and-shut case. There are others who may believe they have something to gain from a civil war in Iraq: Iraqi factions looking to establish their own power, or neighbouring regimes. The dominant Wahhabi sect in Saudi Arabia is ideologically opposed to Shia Islam.

But if causing strife between Iraq's Sunni and Shia was the plan, it hasn't worked so far. There has been remarkably little sign of Shia anger towards them. Most of the Iraqi Shia we spoke to believe al-Qa'ida was behind the attacks, but they don't associate the Sunni extremists of al-Qa'ida with the Iraqi Sunnis.

All the talk from the Americans about civil war has backfired badly among Iraqis. Many Iraqis believe, however misguidedly, that the Americans actually want Sunni-Shia conflict as an excuse to keep their troops in Iraq. In the wake of the Ashoura attacks, it has been the Americans who keep warning of civil war, not Iraqis. A few Iraqis even believe that the Americans may have staged the attacks in Karbala and Baghdad themselves.

So much anger is simmering among the Shias against the occupiers that there is a real possibility the Ashoura attacks may set off Shia resistance against the Americans, of which there has been little so far. From the Shias' leaders the criticism of the Americans has been stinging. As the occupying power, US forces are responsible for security in Iraq, the Iraqi Shias' spiritual leader, Ayatollah Ali al-Sistani, has said. They have created a dangerous security vacuum in Iraq in which groups carrying out suicide bombings and other attacks against Iraqi civilians have been allowed to flourish.

And it is true that the Americans seem inadvertently to have provided militants such as al-Qa'ida the perfect theatre of operations inside Iraq. It is disingenuous for senior US administration figures, like Donald Rumsfeld, to suggest, as they have, that al-Qa'ida was already operating in Iraq before the invasion. The odd militant such as Zarqawi may have been inside Iraq, but they had no freedom to mount spectacular attacks like those at Karbala and Baghdad.

But while we are all concentrating on the effects inside Iraq, I suspect that what happened may have been about more than just Iraq. Within hours of the attacks, Shia marching for Ashoura in Quetta, Pakistan, were gunned down in the streets.

Karbala is a spiritual centre for Shia all over the world, not just in Iraq, and the streets that day were full of Iranians, Pakistanis, Lebanese, even Afghans. More than 40 Iranians were among the dead. And millions of Shia across the world watched this assault on all that is holy to them on television.

The attacks came at a time when Iraq's Sunni are very nervous, as they see the Shia majority beginning to claim power for themselves. The Shia closed the streets of Baghdad for Ashoura marchers, even as their representatives on the US-appointed Governing Council demanded the presidency under the new constitution, to reflect their numbers.

But Sunni Muslims outside Iraq are also nervous at Iraqi Shia demands for power. A Shia-dominated Iraq, neighbouring already Shia-ruled Iran, would drastically alter the balance of power between Sunni and Shia in the Muslim world. It is possible that the screaming all around me in Karbala last week was supposed to echo well beyond the borders of Iraq.