At least 19 outlaws were killed in clashes with troops in Mexico's northeastern state of Tamaulipas, near the US border, where 72 migrants were massacred last month, the army said Thursday.
The clashes, on a road near Ciudad Mier, lasted several hours late Wednesday, as most of the country celebrated 200 years of the start of its independence from Spain with massive parties and firework displays.
An army official said the clashes began after troops followed up on an anonymous call about a fake roadblock.
The victims were unidentified armed men wearing official uniforms, he said.
Corruption is rife among Mexican police and some security forces, while criminals often use stolen, loaned or out-of-date official uniforms.
The clashes occurred in a region where a split between the Gulf drug gang and its former hitmen the Zetas has led to an eruption of violence this year.
First reports said late Wednesday that eight had died in the latest violence.
At least 25 suspected gang members died in a shootout with the military in the same region at the start of the month.
President Felipe Calderon led independence celebrations on Wednesday and Thursday as he was under increasing scrutiny for his military crackdown on organized crime launched three and a half years ago.
More than 28,000 people have died in suspected drug violence since then, according to official figures.