Vote on Sunday in violence-ravaged state elections

Sunday's local polls in 14 out of 31 states, include 12 for governors.

During the campaign, mayoral candidates were killed in Tamaulipas and Chihuahua states, with threats against candidates in others.

The vote is expected to serve as an unofficial referendum on President Felipe Calderon's clampdown on drug violence.

In the highest-level election-related attack in more than a decade, gunmen on Monday killed Rodolfo Torre, the candidate tipped to become governor in Tamaulipas state, which borders Texas.

Immediate suspicion fell on the country's warring drug gangs, and Calderon blamed "organised crime" for the deadly ambush on campaign vehicles.

Analysts forecast high abstention in regions where there is a strong presence of organised crime, which is widespread in Mexico.

Several states holding elections are notorious for bloodshed, including Chihuahua, home to the murder capital of Ciudad Juarez, and Sinaloa, the cradle of Mexico's ever-powerful drug-trafficking industry.

Growing attacks on political candidates, including the still unsolved kidnapping of an ex-presidential candidate in May, have beed added to drug wars in which police, soldiers and innocent bystanders have long been targeted.

Almost 23,000 people have died in drug-related violence seen since Calderon launched a military offensive on organised crime when he took office three and a half years ago.