At least 13 people were killed in three separate clashes between Mexican marines and gunmen in the border city of Matamoros, officials said.
Matamoros is across the border from Brownsville, Texas, and is in an area that is being fought over by the rival Gulf and Zetas drug cartels.
The government of Tamaulipas state says the three gunbattles occurred on Sunday when gunmen attacked troops in different parts of Matamoros.
Its statement describes the attackers only as “armed civilians” and doesn’t say if the gunmen are suspected of belonging to cartels.
Officials said one woman was among the 13 dead civilians.
No marine casualties have been reported.