A roadside bomb killed three American soldiers and injured a fourth serviceman north of Baghdad, the US military said Sunday. The soldiers were conducting a patrol to clear a route so that another unit could move through the area on Saturday, the military said in a statement. A bomb exploded near one of their vehicles, the statement said. The toll raised to 57 the number of Americans killed in Iraq in December. At least 2,945 members of the US military have died since the US-led invasion in March 2003, according to an Associated Press count.