Iraq's top Shia cleric warns of 'genocidal war'

So far he has persuaded most of his followers not to respond in kind against the Sunni, from whom the bombers are drawn, despite repeated massacres of Shia. But sectarian divisions between Shia and Sunni are deepening across Iraq after the killing of 18 children in the district of New Baghdad last week and the death of 98 people caught by the explosion of a gas tanker in the market town of Musayyib. Many who died were visiting a Shia mosque.

There are also calls for the formation of militias to protect Baghdad neighbourhoods. Khudayr al-Khuzai, a Shia member of parliament, said the time had come to "bring back popular militias". He added: "The plans of the interior and the defence ministries to impose security in Iraq have failed to stop the terrorists."

Against the wishes of the Grand Ayatollah, who has counselled restraint, some Shia have started retaliatory killings of members of the former regime, most of whom but not all are Sunni. Some carrying out the attacks appear to belong to the 12,000-strong paramilitary police commandos. Mystery surrounds many killings. A former general in Saddam Hussein's army called Akram Ahmed Rasul al-Bayati and his two sons, Ali, a policeman, and Omar were arrested by police commandos 10 days ago. Omar was released and one of his uncles paid $7,000 for the release of the other two. But when he went to get them he saw them taken out of a car and shot dead.

Fear of Shia death squads, perhaps secretly controlled by the Badr Brigade, the leading Shia militia, frightens the Sunni. The patience of the Shia is wearing very thin. But their leaders want them to consolidate their strength within the government after their election victory in January.

The radical Shia leader Muqtada al-Sadr, whose Mehdi Army militia twice fought US troops, has called for restraint. "The occupation itself is the problem," he said. "Iraq not being independent is the problem. And the other problems stem from that - from sectarianism to civil war. The entire American presence causes this."

The suicide bombings show increasing sophistication. The casualty figures from Musayyib were so horrific because the bomber blew himself up beside a fuel tanker which had been stolen two days earlier and pre-positioned in the centre of the town.