The U.S. military conducted more than five times as many airstrikes in Iraq last year as it did in 2006...The U.S.-led coalition dropped 1,447 bombs on Iraq last year, an average of nearly four a day, compared with 229 bombs, or about four each week, in 2006...The greater reliance on air power has raised concerns from human rights groups, which say that 500-pound and 2,000-pound munitions threaten civilians, especially when dropped in residential neighborhoods where insurgents mix with the population.