(CNN) -- Three separate clashes between soldiers and gang members near the U.S. border in Mexico left a dozen people dead and 21 injured, authorities said.
At least seven of the injured were in grave condition, according to authorities.
The fatalities in the Friday attacks are believed to be nine gang members, two civilians and one soldier, Mexico's Interior Ministry said. They occurred in the municipality of Nuevo Laredo, Tamaulipas.
Interior Ministry officials condemned the attacks as "cowardly acts by organized criminals."
During the clashes, alleged criminals shot at the army and blocked dozens of streets with trailers and trucks, state-run Notimex news agency reported.
The U.S. consulate in Nuevo Laredo issued a warning to citizens to stay indoors until security improves. Consulate officials said there were reports of widespread violence in the area, including carjacking and grenade attacks.
Friday's attacks come a day after a car bomb killed four in Ciudad Juarez and sparked fears of escalated violence throughout the border states.