BAGHDAD - A truck bomb killed 10 people and wounded 37 others when it exploded early on Wednesday morning in a wholesale vegetable market in southern Baghdad, police said.

The bomb, planted in a pickup truck, shook the mainly Sunni Arab area of Doura at around 7 a.m., as merchants wound up the morning's delivery of goods from the countryside.

Doura, like other parts of Baghdad, was once controlled entirely by Sunni Islamist al Qaeda before they were weakened by U.S. and Iraqi forces allied with local Sunni Arab militamen.

Reuters TV footage showed shocked residents gathering around a wreckage of burned, twisted metal and blood stains. Some stared in silence at the carnage. Others shouted in anger.

The bomb slaughtered ordinary people ... grocers and farmers. What did they do wrong? cried one man, who identified himself only as Ali.

He said police had warned the day before that they were expecting a bomb attack in the area.

If so, why didn't they stop the truck at the gate using their bomb detectors? he shouted.

The office of Baghdad security spokesman, Major General Qassim Moussawi, said police had defused a second bomb in the same area.

Sectarian violence has dropped sharply across Iraq, but a spike in major bombings in recent weeks has raised questions about security gains as U.S. combat troops prepare to withdraw from Iraqi cities next month and Iraq gears up for national elections by early next year.

In April, 290 Iraqi civilians were killed in attacks, the highest number since November. Many of the attacks targeted congregations of Shi'ites, many of them religious pilgrims.

Thirteen U.S. soldiers were killed in combat in April.

Earlier this week, Admiral Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, said the recent violence was not likely to alter the U.S. plan to withdraw all U.S. combat troops from Iraq late next summer. Under a bilateral security pact, all U.S. troops must leave by the end of 2011.