CULIACAN, Mexico — Two candidates in a local election in the state of Sinaloa, home to Mexico's most powerful drug cartel, have dropped out of the race after a member of their coalition was shot to death, campaign officials announced Friday.

Lucas Lizarraga, campaign coordinator for the coalition "Together You Win," which groups the leftist Democratic Revolution Party and Workers Party with the conservative National Action Party, said the candidates for mayor and state congress in the town of Sinaloa de Leyva are asking electoral official to postpone the July 7 election because authorities are not ensuring their personal safety.

"Candidates have received threats from organized crime groups and there is a risk of more casualties over the remainder of the campaign and on election day," Lizarraga said.

On Monday, authorities found the body of a 26-year-old who was running for the city council of the same town. Eleazar Armenta was shot to death in the village of Baburias.

Sinaloa state electoral authorities said the candidates missed the deadline to drop out of the race and that their names would appear on the ballot even if they stop campaigning.

"In case one of the applicants who are requesting to withdraw from the race is elected, they can take office since their registration can no longer be invalidated," said Jacinto Perez, president of Sinaloa state electoral council.

The announcement in Sinaloa comes a day after the leader of the Democratic Revolution Party, or PRD, in the southern state of Oaxaca was found slain.

The Oaxaca attorney general's office said the body of Nicolas Estrada Merino, 32, was found Thursday in a sugar cane field near the city of Tuxtepec. It said in a statement that Estrada had three gunshot wounds to the head and that investigators are looking into the circumstances of his death.

The PRD's national leadership condemned the killing and demanded that authorities speed the investigation. They would not say if they thought his killing was election-related.

"I don't want to say if this was political or party-related. We have to be cautious," Miguel Barbosa, PRD coordinator in the federal Senate, said Friday. "Clearly we're talking about a scenario of risk for those in politics. But it doesn't help us right now ... to make declarations that are going to provoke tension and fear among citizens who are going to have to express themselves through their votes on July 7."

Local elections for state representatives and mayors will be held July 7 in 14 of Mexico's 31 states.

The state of Oaxaca has been led since 2010 by a governor representing a coalition between the PRD and the National Action Party.

Estrada was missing for more than two weeks. His car was found burned on July 16. Authorities estimate that he has been dead for some time because only his bones were discovered.

Attacks on local elected officials or candidates are not uncommon in Mexico, especially during election seasons.

In the southern state of Chiapas, police arrested a mayoral candidate for the shooting death of a rival party member last year, and a candidate in the southern state of Guerrero was slain outside his home.

Drug cartels have also orchestrated attacks on politicians. The highest profile was the ambush killing in 2010 of Rodolfo Torre, gubernatorial candidate in the northern state of Tamaulipas.