The US has said it will give Mexico access to an electronic database to trace weapons smuggled from the US to powerful drug gangs across the border.
Mexican police have been fighting heavily-armed drugs gangs
US Attorney General Michael Mukasey said Mexican police who seized arms could use the system to notify the US who would then target the dealers.
Mexico has been struggling to deal with heavily-armed drug traffickers.
It has complained that its northern neighbour is not doing enough to stop the flow of illegal arms into Mexico.
Mr Mukasey also urged the US Congress not to be distracted by the presidential election and approve the proposed $1.4bn (£712m) joint US-Mexican anti-drug plan, known as the Merida Initiative.
Speaking during his official visit to Mexico, Mr Mukasey said the e-Trace database would be installed at US consulates across Mexico to help local police track gun dealers back in the US.
He said US officials would then be able to "target that dealer".
"Inevitably we'll find people who are not doing what they ought to do, and they'll be prosecuted," Mr Mukasey said.
Mexican Attorney General Eduardo Medina Mora welcomed the announcement, describing it as "indispensable that we establish common criteria to solve this issue".
Mr Mukasey also said the US authorities had hired more firearms agents to check the records of gun dealers along the border.
Separately, Mr Mukasey revealed that Washington and Mexico had discussed recent incidents near Mexico's border city of Tijuana in which US border patrol agents fired tear gas into Mexican territory.
The US says the agents acted to protect themselves against rocks being hurled at them from across the border, describing the clashes as drug-related.
"We're trying to deal with it. We've talked to the Mexicans about it, and they're trying to deal with it," Mr Mukasey said.
"What happens is that there is organised rock-throwing to divert border guards, who then become involved in whatever exchanges they're involved in, then you get a bunch of backpackers running across the border with backpacks full of marijuana," Mr Mukasey said.