Fifteen shot dead at Mexico ranch

The body of Margarito Montes, an organiser of agricultural workers, was among those found riddled with bullet holes in southern Sonora state.

Correspondents say the killings bear the hallmarks of drug gang murders, but the link has not officially been made.

More than 15,000 people have died in drug-related violence since a concerted push against drug gangs began in 2006.

President Felipe Calderon has so far deployed some 45,000 extra security forces in key areas across Mexico in a bid to tackle the cartels.

Correspondents say farmers are often caught up in drug violence, by being paid or coerced to grow marijuana and opium poppies.