Some 500 bodies still remain to be uncovered from hidden graves in the northern Mexican state of Tamaulipas, a non-governmental group told reporters on Tuesday.

Isabel Miranda de Wallace said her NGO, which fights Mexico's rampant kidnapping, had gathered data from a recent visit to San Fernando, a small town near the US border, including interviews with gang suspects.

The region is largely dominated by the notorious Zetas gang -- which controls drug trafficking routes into Mexico's northern neighbor -- and has been the site of numerous massacres over the past year.

A total of 193 bodies have already been uncovered from clandestine graves around San Fernando in recent months, in the same area that saw the massacre of 72 migrants last year.

More than 41,000 people have died in violence linked to Mexico's organized crime gangs since President Felipe Calderon launched a military crackdown on them in December 2006, according to media counts and official figures.