US seeks Mexico border gun sales details
Weapons dealers in the south-west US will be required to report large sales of some semi-automatic firearms to help stem the flow of weapons into Mexico.
Under a new US government rule, authorities must be contacted when more than two semi-automatic rifles with detachable magazines are purchased.
The weapons are reportedly sought after by drug-trafficking organisations operating inside Mexico.
The rule will affect dealers in Texas, California, Arizona and New Mexico.
The regulation will require dealers to contact the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) if one individual purchases more than two semi-automatic rifles, within a five-day period, that accept detachable magazines and use ammunition larger than .22 caliber.
The ATF first unveiled its proposal for the new rule in December 2010.
"The international expansion and increased violence of transnational criminal networks pose a significant threat to the United States," Deputy Attorney General James Cole said in a statement.
Mr Cole said the weapons targeted by the regulations are "highly sought-after by dangerous drug trafficking organisations and frequently recovered at violent crime scenes near the south-west border".
He added that the new rules would help authorities "detect and disrupt the illegal weapons trafficking networks responsible for diverting firearms from lawful commerce to criminals and criminal organisations".
Meanwhile, the the National Rifle Association has vowed to sue the Obama administration over the new regulation.
"They don't have the statutory authority to do it, and we'll file a lawsuit as soon as the first letters are sent" demanding the sales information from dealers, the NRA's legislative director Chris Cox told Politico.Fast and Furious
The announcement comes amid an ongoing outcry over a botched operation to track the illegal movement of guns to Mexico.
Operation Fast and Furious saw US agents allowing hundreds of guns into Mexico illegally with the hope of tracking them to major arms dealers.
Kenneth Melson, acting head of the ATF, has come under pressure to resign over the sting carried out by an Arizona-based branch of the agency.
Mr Melson told members of Congress last week that he had not known about the operation until it became public and that the department of justice (DoJ) had tried to prevent him from co-operating with the inquiry.
President Barack Obama has said it would not have been "appropriate" for the ATF to allow weapons to be smuggled into Mexico.
In January, the Mexican government released figures suggesting that at least 34,612 people had died in drug-related violence in Mexico since December 2006.
There is speculation the figure may now have passed 40,000.