The attackers wielded high-caliber guns and rode aboard 10 armored trucks in the 3 a.m. ambush on Sunday close to the U.S.-Mexico border, the Nuevo Leon security ministry said.
"Sadly, six members of our unit lost their lives in the line of duty," the ministry said in a statement, adding that the police had acted "heroically."
Four other officers were injured and receiving medical attention, the ministry said.
President Andres Manuel Lopez Obrador inherited a nation reeling from a high murder rate and has struggled to rein in entrenched gang violence. Average annual homicide totals are on track to be the highest under any Mexican administration since modern records began.
The recent killing of two Jesuit priests and a tour guide in the northern state of Coahuila drew condemnation from Pope Francis, who lamented "so many killings in Mexico."