A massive car bomb ripped through a crowd of evening shoppers in a busy Baghdad, killing 51 people and wounding more than 70, the deadliest strike in the Iraqi capital in months.

As US generals pointed to the fragile security gains in Iraq, terrorists sent a pick-up filled with explosives into the mainly Shia area of Hurriyah in northwestern Baghdad in a move designed to reignite the sectarian tensions that once tore the city apart.

Many of those killed were trapped in a burning building that went up in flames when the powerful blast set fire to a generator supplying the area with electricity, witnesses said. Others died when a multistorey building collapsed from the shock of the explosion, which set fire to more than a dozen other buildings.

The explosion, the deadliest in the capital for three months, showed that despite the progress made by the US ‘surge’ and an increased presence of Iraqi armed forces o the streets, bombers are still waiting to strike at any moment. The attack bore the hallmarks of al-Qaeda, who have killed thousands of Shia civilians in bombings so vicious that they eventually turned its local Sunni insurgent allies against it in many parts of the country.

“The blast occurred because there wasn't any security presence by the Iraqi army or police at the scene, not even any checkpoint,” said local resident Khalid Hassan, who was wounded in the blast. “We are all victims of terrorism and carelessness.”

The explosion was the second to shatter the relative calm in one day. Earlier, a bomb hidden on a motorcycle exploded at a checkpoint in northern Baghdad, killing four fighters from a Sahwa, or Awakening group, the Sunni militias that have formed to combat al-Qaeda in Iraq. The terrorist organization has been increasingly targeting such groups, many of whose members are former Sunni insurgents who once fought alongside al-Qaeda against US forces.

The bombings were the deadliest attacks since early March, when two women suicide bombers, believed to have mental problems, blew themselves up in Baghdad’s pet markets, killing 68 people.

Although US and Iraqi forces have largely driven al-Qaeda from its former bastions in western Baghdad, and are now battling its die-hard elements in the northern city of Mosul, the organization has proven to be tenacious and determined to carry out the kind of attacks that drove the country to the brink of all-out civil war.

Endless car bombings led to the rise of the Shia militia, the Mahdi Army, to protect Shia areas, but the movement quickly started launching punitive raids into Sunni areas, killing civilians and guerrillas alike and ethnically cleansing large areas of the capital. This latest attack came as the Mahdi Army’s commander, the rebellious cleric Moqtada al-Sadr, announced that he was reducing the armed wing of his sprawling militia and ordering large parts of it to stand down its military activities.

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