Troops in Mexico pursued and shot dead 12 people after coming under attack in Zacatecas state, officials have said.
The clash happened when soldiers tried to stop suspect vehicles and the occupants opened fire, leading to a chase for 50km (31 miles).
Several people were arrested and a number of weapons confiscated.
Earlier, the Mexican Navy said it had arrested 18 drug trafficking suspects in Zacatecas, including 12 boys and a woman with a baby.
A navy statement said the group was detained on 31 December in the town of La Estacion.
The suspects were carrying several weapons, two grenade launchers and packets of marijuana and cocaine.
On Wednesday, soldiers patrolling in Rio Grande came under fire when they tried to detain armed suspects, officials said.
Ten men and two women were killed in the clash.
Zacatecas, located in central Mexico, lies on key drug trafficking routes.
More than 60,000 people have died in drug-related violence in Mexico since late 2006 when the previous government deployed troops to take on the drug gangs.
President Enrique Pena Nieto, who took office on 1 December, is aiming to create a new national militarised force to take over policing duties from the military, although there is, as yet, no timescale for this.
