"God is Great," screamed a man seconds before he blew himself up, killing 10 people in a restaurant in Ramadi, the capital of Anbar province in western Iraq. A series of suicide bombings have shown over the past week that al-Qa'ida in Iraq, though battered by defections over the past year, is striking back remorselessly at Sunni Arab leaders who ally themselves to the US.

In another attack in the village of Albu Mohammed, south of Kirkuk, an elderly man thought by guards to be too old to be a bomber, walked unsearched into a tent filled with mourners attending the funeral of two Sunni tribesmen who had been killed after they joined al-Sahwa, the Awakening Council, as the pro-US Sunni group is called. The man detonated the explosives hidden under his long Arab robes, killing at least 50 people.

A vicious civil war is now being fought within Iraq's Sunni Arab community between al-Qa'ida in Iraq and al-Sahwa while other groups continue to attack American forces. In Baghdad on a single day the head of al-Sahwa in the southern district of Dora was killed in his car by gunmen and seven others died by bombs and bullets in al-Adhamiya district.

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US spokesmen speak of a "spike" in violence in recent weeks but in reality security in Sunni and Shia parts of Iraq has been deteriorating since January. The official daily death toll of civilians reached a low of 20 killed a day in that month and has since more than doubled to 41 a day in March. The US and the Iraqi government are now facing a war on two fronts.

The attack in Ramadi shows al-Qa'ida still has support in Anbar province where al-Sahwa was founded and has greater strength in Diyala, Salahudin and Nineveh provinces. In Sunni parts of Baghdad, al-Sahwa often includes members of al-Qa'ida whose loyalties have not changed or gunmen who think it safest to work for the US and al-Qa'ida. "No officer in al-Sahwa walks home unless he has a relationship with al-Qa'ida," said one al-Sahwa member. "It would be too dangerous for him otherwise."

The American-backed government of Nouri al-Maliki is in the meantime stepping up its campaign against the Mehdi Army militia of the anti-American cleric Muqtada al-Sadr. Iraqi troops sealed off the Basra office of the Sadrists yesterday. "Troops from the Iraqi army prevented us from holding Friday prayers and now they are cordoning off the office," said Harith al-Idhari, the head of the office. "They want to storm it and clear everybody out of it."

Mr Maliki is convinced that this is the moment to assert himself against the Sadrists despite military setbacks when he launched his offensive against Basra on 25 March. Two brigades of about 600 men, each from the army's 14th Division whose soldiers come from the city, refused to fight the Mehdi Army as did most of Basra's 11,000 police.

The Iraqi government says that it has purged 1,300 men from its armed forces and police since the Basra operation and is willing to try again against the militiamen. But it has only been able to hold its own in Basra, Baghdad and other cities because of backing from the US.

The Sadrist office in Basra is housed in the building of the old Olympic committee. "We have orders to take back all the government buildings that are occupied by parties and political movements in Basra within 48 hours," said the Interior Ministry spokesman Major-General Abdul Karim-Khalaf.

The greatest stronghold of the Sadrists is Sadr City in Baghdad, which has a population of two million and is virtually a twin city to the capital. US forces have now started building a concrete wall which will seal off the southern part of Sadr City. The US and the Iraqi government are particularly keen to gain control of those parts of Sadr City used to lob rockets and mortars into the Green Zone.

Despite government purges, it is still unclear how far Iraqi army units are willing to fight Shia co-religionists. Yesterday a company of government troops abandoned their positions in al-Nasir police station in Sadr City when they came under attack from militiamen during a sandstorm. Another company had deserted earlier in the week.

Mr Maliki is eager to show that the Iraqi government is strong enough to overcome its domestic enemies, but the fighting against al-Qa'ida in Iraq in Sunni districts and the Mehdi Army in Shia areas over the past month has proved the opposite. The Iraqi army has appeared as dependent on American support as it ever was in the past.