(CNN) -- Attackers shot a mayor-elect at least five times at a veterinary clinic in a Mexican border state Friday night, officials said.

Ricardo Solis Manriquez was in critical condition at a local hospital after one of the bullets hit him in the head, said Carlos Gonzalez Estrada, a spokesman for the attorney general's office in Chihuahua.

Solis, the mayor-elect of the town of Gran Morelos, was scheduled to take office October 9.

The shooting was the latest in a string of attacks against elected officials in Mexico, where at least four mayors have been killed in the past two months.

A leading gubernatorial candidate also was killed in late June.

On Thursday, authorities said gunmen killed Prisciliano Rodriguez Salinas, the mayor of Doctor Gonzalez, a small town in the border state of Nuevo Leon.

Political parties in Mexico were quick to condemn the violence.

"Both events, the latest in a chain of episodes of violence that threaten to destabilize the rule of law in many cities of the country, cannot go unpunished and demand an immediate response," said Hortensia Aragon, general secretary of the left-wing Party of the Democratic Revolution.

Aragon said in a statement that the attacks were "cases that exemplify that the Mexican political class has once again become cannon fodder due to the inability of the federal government to contain the violence that prevails in our country."

President Felipe Calderon condemned the Nuevo Leon attack. And his National Action Party also issued a statement asking state authorities to investigate and punish those responsible.

Authorities have said drug cartels were suspected in earlier deaths of the politicians, a relatively recent development in the government's bloody war on organized crime that has seen more than 28,000 people killed in less than four years.

But Nuevo Leon State Attorney General Alejandro Garza y Garza told reporters Friday that the death of Rodriguez, who was killed on his ranch Thursday, might not be connected with organized crime, state-run news agency Notimex reported.

"The form of operating is not directly how organized crime does it, so we could be dealing with another type of event," he said.