Gunmen ambushed four leftist politicians in two separate attacks in southwestern Mexico, injuring three of them, authorities said Monday. The body of a fifth political leader was found burned in the trunk of a car a month after he was kidnapped.

Police had not established a motive for the attacks in Guerrero, a coastal state long mired in drug and political violence. But a local official with Mexico's main leftist party said he feared they were part of an intimidation campaign ahead of July 5 legislative elections.

"We think it's an attempt to intimidate citizens and prevent them from voting in July," said Martin Hernandez, leader of the Democratic Revolution Party, or PRD, in Acapulco. "Every election period there is violence, and the worst part is that we get used to living like this."

Gunmen in a vehicle intercepted a car carrying three PRD members Monday in the town of Arcelia, the Guerrero state Public Safety Department said in a statement. One of the gunmen opened fire, wounding all three politicians, who were hospitalized. The three included Nicanor Adame Serrano, who is running for a congressional seat in the July elections, and his campaign manager.

The body of another PRD member, Alvaro Rosas, was found in the trunk of a car Sunday in Tecpan de Galeana, a coastal town about halfway between the resort cities of Zihuatanejo and Acapulco, said Delfino Vargas, a state police officer.

Rosas, the leader of the PRD in the town, had been kidnapped April 23. A threatening message was found near his body, Vargas said.

In a separate attack, gunmen opened fire on a vehicle carrying Manuel de la Barrera, a congressional candidate for the Socialist Democratic Party, the Public Safety Department said. De la Barrera was unharmed but his driver was wounded in the weekend attack just outside of Acapulco.

Authorities did not know if the attacks were linked.

Political violence is common in Guerrero, where leftist rebels have fought for three decades and drug cartels are waging a bloody battle for turf.

The PRD, mired in internal strife, is struggling to hold onto Guerrero state. Last year, PRD mayoral candidates lost Acapulco and Zihuatanejo to the Institutional Revolutionary Party, or PRI, which ruled Mexico for 71 consecutive years until it was ousted nine years ago by the conservative National Action Party, or PAN.

The PAN, which currently governs Mexico under President Felipe Calderon, is also expected to lose ground in July voting amid a steep economic recession and organized-crime violence that has claimed more than 10,750 people since Calderon took office in 2006.

On Monday, the bodies of six people were found burned in a car in Miguel Aleman on the Yucatan Peninsula, authorities said. Police were still trying to identify the bodies.