Mexico sent a diplomatic note to the US government on Monday demanding information on whether Mexican government officials knew about the failed 2009-2010 Fast and Furious gun-tracking operation.
Mexico's Foreign Relations Department said in the note that if Mexican officials were aware of the scheme, as some testimony suggests, then they violated the country's laws.
But if Mexico wasn't advised of the operation, then Mexico's sovereignty would have been violated by US agents, the department said.
In the scheme, US federal agents allowed criminals to buy firearms with the intention of tracking them to criminal organizations.
But the US Bureau of Alcohol, Tobacco, Firearms and Explosives lost track of most of the guns, including two found at the scene of the 2010 killing of a US Border Patrol agent.
Authorities who conducted the investigation faced criticism for allowing suspected gun buyers for a smuggling ring to walk away from gun shops in Arizona with weapons, rather than arrest them and seize the guns.
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The investigation's failures were later examined in US congressional hearings.
Many of Mexico's drug gang killings are carried out with weapons smuggled in from the United States; the operation had been meant to stem that flow.
The diplomatic note said: The Mexican government asks to be given all the available information on the Fast and Furious Operation, in the framework of cooperation and mutual trust that characterizes the close relations between our two countries.