Mexico said Monday that US military weapons had been detected entering the Latin American nation, which blames firearms trafficking from its northern neighbor for fueling drug cartel-related violence.
The Mexican defense ministry has alerted Washington about inflows of arms that are supposed to be "for the exclusive use of the US army," Foreign Minister Alicia Barcena said at a news conference.
"It's very urgent that an investigation be carried out," she added, without give more details.
The arms smuggling was one of the issues discussed by the two countries in Washington on Friday during a visit by Barcena and other senior Mexican officials, she said.
Mexico has long pointed the finger at the United States and its lax gun laws for the flow of weapons to its cartels, which in turn are often funded by selling drugs to US consumers.
The Mexican government has filed two lawsuits in US courts against the firearms industry.
The US ambassador to Mexico, Ken Salazar, told reporters on Monday that reducing weapon flows from the United States to Mexico was a priority for President Joe Biden.
"We know that 70 percent of the weapons that cause violence here in Mexico come from the United States," he said.
More than half a million weapons are trafficked into Mexico from the United States annually, according to authorities in the Latin American nation.
Mexico tightly controls weapons sales, making them practically impossible to obtain legally, but drug-related violence involving firearms remains widespread.
There have been more than 420,000 murders since 2006 when the Mexican government deployed the military to fight drug trafficking, most of them blamed on criminal gangs.