Mexico is experiencing a surge in violence, with journalists among the victims, amid a presidential campaign, with no end in sight to the killing as rival cartels battle each other and impunity prevails in the country.

The massacres of the past few weeks are "clear signs" of the conflict between the Sinaloa and Los Zetas drug cartels "in their attempt to control sales sites and (smuggling) routes for their criminal businesses," Government Secretary Alejandro Poire said Monday.

Mexico has been rocked recently by the discovery of 49 mutilated bodies on the side of a road in the northern state of Nuevo Leon, the discovery of 18 bodies on a road near Guadalajara, Jalisco, and 23 other corpses found in Nuevo Laredo, a border city in Tamaulipas state.

The massacres are related to the war being waged by the Sinaloa and Los Zetas cartels, Mexico's "most important" criminal organizations, Jorge Chabat, an expert on organized crime groups, told Efe.

"The cartels are expanding and they are running into each other, and they are settling control of territory the only way they know how, with this violence," Chabat said.

To a great extent, Los Zetas "are the ones who have caused this spiral of violence in recent years," Chabat said.

The Zetas are dedicated to "kidnapping, extortion, people trafficking, collecting protection money (and) murdering people," while the Sinaloa cartel "is more traditional. They kill their rivals, but there is no evidence that they are involved in other types of crimes," the expert said.

There is no "direct link between the electoral process" and the surge in violence, Chabat said, adding that President Felipe Calderon's strategy of taking on the cartels by deploying soldiers in the streets "has functioned badly, but there was no other option."

"I don't see a way out in the short term," Chabat said, noting that the state lacks effective instruments and institutions to deal with the problem.

None of the candidates vying for the presidency have proposed a "radical change" in Mexico's security strategy, Chabat said.

Journalist Marco Lara, another expert on drug trafficking, said the wave of violence was "foreseeable" given that Calderon used the term war to define his security policy.

The surge in violence as the July 1 presidential election draws closer may be attributable to the cartels' "enormous awareness and management of political timing," Lara said.

Presidential candidates Enrique Peña Nieto, Andres Manuel Lopez Obrador, Josefina Vazquez Mota and Gabriel Quadri have been "very cautious because they do not want to distance themselves from the White House's expectations," Lara said.

The increasing violence aimed at journalists is "terrible, intimidating. It's nothing less than a radicalization of what has been happening," Lara said.