A huge blast tore through a section of downtown Nashville early Friday, after police responding to reports of gunfire discovered a parked motorhome reportedly blaring a warning that it carried a bomb. The explosion shattered windows and ripped apart trees but appeared calculated to spare lives, injuring just three people as it detonated at 6:30am (1230 GMT) in a section of the southern US city that was largely deserted due the early hour and the Christmas Day holiday.