More than 50 mourners were killed in northern Iraq today when a suicide bomber blew himself up at the funeral of two Sunni tribesmen, who had turned against al-Qaeda, in one of the bloodiest attacks so far this year.

The attack came two days after 60 people died in a wave of bombings in Sunni Arab areas to the north and centre of the country, raising fears that al-Qaeda is regrouping after a period of relative calm.

Wearing a suicide vest, the bomber walked into a tent where mourners had gathered to pay their last respect to the two tribesmen, who were murdered yesterday. He detonated his explosives among the crowd, killing and maiming scores of people.

"Suddenly a fireball filled the funeral tent. I fell to the ground. I saw bodies scattered everywhere," said Ali Khalaf, one of about 50 people wounded in the blast, which happened in the Sunni Arab village of Albu Mohammed in restive Diyala province.

At least 51 people were killed, said a police officer, who gave his name as Captain Othman.

Pickup lorries ferried many of the injured to a hospital in the nearby city of Kirkuk. Outside the hospital, frantic relatives gathered to search for loved ones. Women clad in black robes sat on the ground, wailing in grief.

Police officers said that al-Qaeda had warned mourners against holding a large gathering, but the ceremony went ahead all the same.

The funeral had been for two members of a growing group of Sunni tribesmen and former insurgents who have spurned Sunni Islamist al-Qaeda and taken charge of security in their neighbourhood under the payroll of the US military.

The so-called Awakening movement is cited as one of the main factors for a sharp reduction in violence over the past year, but their members, numbering some 90,000, have become favourite targets for extremist militants.

Today’s attack was the deadliest since March 6, when a bombing in the capital killed 68. It also followed Tuesday’s multiple bombings, including a devastating car bomb in Baquba, the provincial capital of Diyala.

US and Iraqi forces have been pushing into Diyala since the start of the year after commanders said that successful operations in and around Baghdad had forced al-Qaeda fighters to move northwards. The bloodshed this week, however, highlights the enduring ability of militants to launch large-scale attacks, the US military said.

“Al-Qaeda Iraq remains a determined and dangerous enemy, with both the will and the capability to indiscriminately kill and maim innocent Iraqis,” Rear Admiral told The Times in an email.

“These attacks also serve as ample evidence that AQI [al-Qaeda in Iraq] recognises both the Iraqi Security Forces and the Sons of Iraq [also known as the Awakening movement] as serious threats,” he said.

Recent weeks have also brought an upsurge in violence between US-Iraqi forces and Shia militias, particularly members of the Mahdi Army loyal to the anti-American cleric Hojatoleslam Moqtada al-Sadr and associated splinter groups.

An offensive launched on March 25 by Iraqi forces against Shia militants in Basra triggered a militia uprising across southern Iraq and in the Mahdi Army stronghold of Sadr City, a Baghdad slum.

This evening, two mortar shells landed in the green zone, the fortified Baghdad district where Iraqi government offices and the US and British embassies are located — the latest in nearly daily mortar volleys usually blamed on rogue Mahdi Army fighters or other Shia militants. There were no reports of casualties.

Away from the violence, people in the Iraqi capital were enduring a different form of suffering after a sandstorm descended on the city from the early hours of the morning. Thick fog-like dust hung in the air all day, forcing scores of people to go to hospital with breating difficulties.

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