Hooded gunmen killed the mayor of a small town in the northern Mexico state of San Luis Potosi, and prosecutors announced the arrest of seven suspects in the massacre of 72 migrants in August.
President Felipe Calderon's office issued a statement on Thursday saying he "energetically condemned" the slaying of the mayor of El Naranjo — the third mayor to be killed in Mexico in less than a month.
Amid the violence, US Secretary of State, Ms Hillary Rodham Clinton, said that Mexico is "looking more and more like Colombia looked 20 years ago, where the narco-traffickers control certain parts of the country, not significant parts."
Her comments raised hackles in Mexico.
"Of course we do not agree with the statement in this regard, given that there are very important differences between what Colombia faced then and what Mexico faces today," Mexican government security spokesman, Mr Alejandro Poire, said.
Mexican officials say drug cartels are not allied with domestic rebel insurgencies, do not have political influence or following and do not exercise formal control of large swaths of the country, as they did in Colombia in the 1980s and 1990s.
But attacks like Thursday's shooting death of El Naranjo Mayor Alexander Lopez Garcia suggest cartels are targeting civilian government in Mexico.
The San Luis Potosi state prosecutors' office said Lopez Garcia was killed by a squad of four hitmen who pulled up in a vehicle.
Two of the attackers burst into Lopez Garcia's office and killed him before fleeing. The rural township of about 20,000 people borders the violent-wracked state of Tamaulipas, where 72 migrants were massacred by drug gunmen in August.
There was no immediate information on the motive in the attack, but the style of the slaying resembles methods used by Mexico's drug cartels.