The two neighboring countries also agreed to cooperate on measures to reduce drug consumption and combat addiction, the Mexican foreign ministry said in a statement.
"A number of advances on the issue of arms trafficking were discussed with the aim of analyzing how to implement operations with non-intrusive technologies in key points of the border to stop movement of arms and ammunition into our country," it said.
In November, U.S. President Donald Trump threatened to designate Mexican drug cartels as terrorist groups after a series of security lapses, including the murder of nine women and children of U.S.-Mexican origin in northern Mexico.
The threat prompted a speedy request for talks by Mexico, and Barr made an initial visit to the country last month.
Meanwhile, Mexico has been preparing a package of judicial reforms that could allow wire taps to be used as evidence in court, as well as measures to limit legal challenges to avoid extradition delays for criminal suspects.Such reforms could facilitate cooperation on security between Mexico and the United States, which under Trump has pressed Lopez Obrador to tighten border security in order to stem the flow of migrants north from Central America.