Husayn al-Shammari, an Iraqi journalist, told Aljazeera: "A car bomb detonated on Wednesday morning in Rabia street in Baghdad, less than 1km from the site where US forces exploded a booby-trapped car on Tuesday.
"The explosion targeted volunteers for the Iraqi National Guards.
"They [the volunteers] arrived on Wednesday morning at the same volunteers' centre where US forces detonated a car on Tuesday. However, citizens of the area prevented them from queuing at the centre, behind al-Mulla Hwaish mosque in al-Rabia street in western Baghdad.
"The volunteers stood 1km away from the centre, near a building called Madinat al-Hasibat," he said.
"A car bomb then detonated in the site next to them," he added.
String of attacks
US Black Hawk crash injured
three crew members
"More than 25 shops have also been destroyed in Madinat al-Hasibat," he said.
As thick black smoke spiralled into the sky and shards of glass and debris littered the street, US soldiers in armoured vehicles cordoned off the area and fire-fighters doused water on burning cars.
There have been several car bomb attacks in the capital over the past two weeks.
"This is the fourth car bomb since Tuesday, indicating security deterioration in the city," al-Shammari told Aljazeera.
Black Hawk down
A US Black Hawk helicopter crashed shortly after take off in southern Iraq, wounding three crew members, the military said.
The helicopter went down on Tuesday night near the city of Nasiriya, 375km south of Baghdad.
"The three crew members sustained minor injuries and the aircraft was severely damaged," a military spokesman said.
The spokesman added a military investigation was underway.
A US soldier was killed in an attack on a patrol in the northern city of Mosul on Wednesday, the US military said, a few hours after another soldier died in a roadside bomb attack in Tikrit, just north of Baghdad.