A 13-year-old girl became Iraq's latest suicide bomber today, killing four people at a security checkpoint in the town of Baquba.

On a day of renewed violence, at least 31 people were killed in a double bombing at a Baghdad market, the deadliest attack to rock the Iraqi capital in months. The attackers first detonated a car bomb in the Sunni district of Adhamiyah, hitting a minibus carrying girls to school. As a crowd gathered to help the girls, a suicide bomber ran in and blew himself up.

The Interior Ministry said that 31 people were killed and 71 wounded in the deadliest to hit Baghdad since June 17 when 51 people were killed in a car bombing in the Al-Hurriya district.

In the Baquba attack, the girl blew herself up at a checkpoint manned by members of the Sunni Muslim 'Awakening' councils, which have led the fight against al-Qaeda in Iraq. Four men, including a leading Sunni militiaman, were killed and 15 civilians wounded.

Witnesses said that the Baghdad attack took place at about 8am (0500 GMT) on a street lined with restaurants and coffee shops popular with Iraqi security forces, as a bus carrying young girls to school drove past.

“There was a huge explosion, and before I went out to look another bomb went off,” said Fadel Hussein, a waiter at a teahouse on Kassra Street, the scene of the bombings. “Heavy smoke was everywhere. There were so many bloody victims on the ground, we helped to evacuate those people to ambulances."

The US and Iraqi military cordoned off the area that was littered with glass and scorched cars as sobbing parents desperately searched for their sons and daughters.

One woman in her 40s and wearing a black abaya, the traditional black Arabic dress, sat on the ground crying uncontrollably. She sobbed: “I’m waiting for my husband who is inside the area looking for my son. I hope he is still alive."

Ahmed Riyadh, 54, owner of a nearby grocery, said the bombing was a “vicious attack" that “did not differentiate between Shi'ites and Sunnis”.

"We are fed up with such attacks and we want only to live in peace,” he said. “The politicians should work hard and set aside their differences to stop the bloodshed.”

The US and Iraqi military cordoned off the area that was littered with glass and scorched cars as sobbing parents desperately searched for their sons and daughters.

One woman in her 40s and wearing a black abaya, the traditional black Arabic dress, sat on the ground crying uncontrollably. She sobbed: “I’m waiting for my husband who is inside the area looking for my son. I hope he is still alive."

Among those killed were three policemen, three women and five children, police said.

Suicide attacks are usually the hallmark of al-Qaeda in Iraq, which continues to have a small presence in Baghdad despite major setbacks after repeated Iraqi and American military sweeps.

Despite the dramatic improvement in security in large sections of Iraq, including the capital, militants continue to launch near daily attacks, most of them targeting US and Iraqi security forces.

Baghdad has been hit by a string of bombings in the past week, most of them small roadside bombs that claimed a handful of victims. The US military says the capital has become much safer since the launch last year of a joint Iraqi-US security plan which cut attacks by about 90 per cent to an average of four a day.

According to the Iraqi military, the number of car bombings in the capital has also fallen sharply, falling from a total of 415 in 2006 to 61 so far in 2008.

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