A parked car bomb exploded in a largely Shiite neighborhood of central Baghdad on Wednesday, police said, killing at least 16 people as the US defense secretary visited the capital to assess whether the downturn in violence in Iraq can be sustained. It was at least the fourth deadly car bomb in Iraq on Wednesday. Earlier in the day, a blast went off in the northern city of Mosul, where Pentagon chief Robert Gates landed on his sixth trip to Iraq. Gunfire and sirens followed the blast in Baghdad's Karradah neighborhood, and a plume of smoke rose to the sky. Police and hospital officials said at least 16 people were killed and 32 wounded in the explosion, which took place across the Tigris River from the Green Zone shortly before a news conference by Gates. Despite continuing violence, the Pentagon chief said he believes "a secure, stable Iraq is within reach" although much remains to be done to counter ongoing violence and ensure Iraqi forces are ready to take over more military duties from US troops.