Photos taken by an ATF agent in Ciudad Juarez show serial numbers and guns seized in Mexico, believed to have been purchased in U.S. (date is unknown)

Story highlights

NEW: Sen. Chuck Grassley says "most of these guns can't be traced to U.S. gun dealers"

70% of guns traced from Mexican criminal activity originated in the United States

All the guns that were traced were passed to the U.S. from Mexican officials

Gun-control advocate said figures are evidence of need for stricter gun laws

Washington CNN  — 

Nearly 70% of guns recovered from Mexican criminal activity during the past five years and traced by the U.S. government originated from sales in the United States, according to data released Thursday by the Bureau of Alcohol, Tobacco, Firearms and Explosives.

All the guns that were traced were passed to the U.S. from Mexican authorities.

ATF Special Agent John Hageman was careful in his comments as he released the data.

“Our job is to provide the aggregate tracing figures and not to speculate,” he said.

Sen. Chuck Grassley, R-Iowa, cautioned against reading too much into the statistics beyond that “most of these guns can’t be traced to U.S. gun dealers” and some could be tied to “the federal government’s own gun-walking scandal.”

“We also have to remember that the only guns Mexico is going to submit for tracing are guns they know are from the United States, which clearly paints an incomplete picture of the firearms found in Mexico,” he said in a statement.

But anti-gun advocates were not so restrained. Sen. Dianne Feinstein, D-California, a leading gun-control voice on Capitol Hill, said the figures are evidence of the need for stricter gun laws.

Some likeminded legislators claim that the National Rifle Association and the gun industry have downplayed the degree to which U.S. gun sales are responsible for weapons used by Mexican drug cartels and other violent criminals south of the border.

The newly released data show that from 2007 to 2011 in Mexico City, the ATF traced 99,691 firearms from their manufacture to the retail point of sale. Of those weapons, 68,161 were U.S.-sourced weapons, the ATF said.

Hageman said a significant trend over the past five years has been an increase in rifles among firearms that Mexico asked the ATF to trace.

“Law enforcement in Mexico now report that certain types of rifles, such as the AK and AR variants with detachable magazines, are used more frequently to commit violent crime by drug trafficking organizations.”

Both the Bush and Obama administrations have been strong supporters of President Felipe Calderon’s efforts to control drug cartels along the U.S.-Mexico border, and both governments have made efforts to try to curtail the illegal movement of firearms across the border to Mexico.

One operation, code-named Fast and Furious, went awry when hundreds of illegally purchased weapons, which were supposed to be tracked, got lost after they crossed the border. Two of the missing guns were found at the scene of the murder of Border Patrol agent Brian Terry in Arizona, resulting in a wave of criticism of the ATF and its parent agency, the Justice Department.