Mexican police arrested four armed men on Monday accused of firing at the mayor's convoy in Matamoros, a northern city bordering Texas in the grips of drug cartel violence.
Mayor Leticia Salazar escaped unscathed from Sunday night's shooting, which took place as she was arriving home in a sport utility vehicle protected by two other vehicles and eight bodyguards, said an official from the Tamaulipas state prosecutor's office.
Herminio Garza, interior secretary of the northeastern state of Tamaulipas, said the gunmen apparently attacked the convoy "by mistake, thinking it was a (rival) group."
The mayor's car was not hit by any bullets, Garza told Milenio television.
But city goverment spokeswoman, Nora Gonzalez, told Milenio that Salazar "felt that it was a direct attack. She is very dismayed at the moment."
The assailants tried to force the mayor's SUV to stop on two occasions, and after it almost rolled over, "they began to shoot at the vehicles," Gonzalez said.
Matamoros is known as a bastion of the Gulf cartel. The city and the rest of the state have been hit by a wave of shootings in recent weeks blamed on infighting among the gang's splinter groups.
Federal police detained four men at dawn on Monday after stopping a suspicious vehicle without license plates and with the lights off.
The suspects confessed to attacking Salazar's convoy, the police said in a statement. Salazar is a member of the conservative and opposition National Action Party.
The shooting came a month after a dummy grenade was tossed in the parking lot of city hall in Matamoros, a city of almost 500,000 across the Texas town of Brownsville.
- Crooked cops -
Salazar faced her own security scandal last year.
In October, nine agents from a special tactical police unit dubbed Hercules Group were questioned over the kidnapping of three American siblings and a Mexican man who were found dead two weeks after their abduction.
Parents of the victims say the mayor's special police unit was behind the crime, but the officers were not charged.
On Sunday, 13 federal police offices were formally arrested on charges of kidnapping a local businessman in Matamoros last week. A 14th officer was released without charges.
The kidnappers had demanded a $2 million ransom for the release of Rafael Gomez Garza, who has since been freed. The man's family accused the officers of committing the crime, according to local media.
The government of President Enrique Pena Nieto stepped up security in Tamaulipas after a series of gun battles last year, putting military generals in full control of police duties.
In a victory of the government, federal forces captured Zetas drug cartel leader Omar "Z-42" Trevino in the neighboring state of Nuevo Leon last week.
The Zetas, founded by military deserters, are former allies of the Gulf cartel but the two gangs split in 2010 and have been at war ever since.