MEXICO CITY, Sept 20 (Reuters) - The death toll from grenade attacks on an independence day celebration in central Mexico rose to eight on Saturday when a 13-year-old died in a hospital after fighting for his life for five days.

Michoacan state Gov. Leonel Godoy told local radio of the latest death from injuries sustained in Monday's attack in the colonial city of Morelia, capital of the drug gang-infested state of Michoacan.

Mexican authorities have blamed drug gangs for the attacks, but no group has come forward to claim responsibility.

The incident appeared to be the first major strike by cartels on ordinary citizens. More than 100 people, including women and children, were wounded.

More than 2,700 people have been killed so far this year in Mexico in a wave of drug-related violence as rival cartels battle each other and security forces.

Mexico is the principal trafficking route for Colombian cocaine to U.S. streets. Mexicans have grown hardened to years of drug violence, but the recent spurt in cartel murders and fatal kidnappings has shocked the nation and triggered protests.

President Felipe Calderon, a native of Michoacan state, has vowed to crush cartel violence and on Thursday announced that the government would start paying rewards to people who turn in organized crime suspects. (Reporting by Chris Aspin, Editing by Patricia Zengerle)

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