A recent surge of violence in Iraq flared up again on Friday when a motorcycle loaded with nails and ball bearings exploded in a crowded Baghdad market, killing 13 people and wounding dozens, Iraqi officials reported. The blast occurred just after 9 a.m., when the the bazaar was crowded with young people buying and selling motorcycles. "I saw a ball of fire and some motorbikes were lifted about 10 meters [yards] into the air," an eyewitness said. "When the smoke from the explosion vanished, I saw a large number of young men lying on the ground soaked in blood." The bombing was the latest in a week of attacks that have killed more than 200 people, in the lead-up to next week's deadline for U.S. troops to withdraw from Iraq's urban areas.