The U.S. was the source of at least 70% of 29,284 firearms recovered by authorities in Mexico in 2009 and 2010, according to new U.S. government figures.

The statistics from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives are expected to add to controversy over the U.S. role in fueling drug-cartel violence in Mexico, which has killed more than 40,000 people since 2006.

U.S....