MEXICO CITY - Seven more mass graves with 47 bodies were discovered at a farm in the northeast Mexican state of Tamaulipas, bringing the total of the bodies found at the site to 193, authorities said Tuesday.

A total of 85 suspects, many affiliated with the Los Zetas cartel, have been arrested in the case, Attorney General Marisela Morales told a press conference.

Investigators now believe the victims found in the mass graves were South American migrants who were kidnapped by Los Zetas in late March as they travelled through Mexico toward the United States.

Tamaulipas, where massacres of migrants had been reported earlier this year, has been mired in violence for more than a year as two drug cartels, Los Zetas and Gulf Cartel, vie to control the state, a transit point for  transporting drugs up to the United States and smuggling weapons back to Mexico. Nationwide, more than 35,000 have been killed in drug-related violence during the past four and a half years.

Morales proposed on Tuesday that federal and state prosecutors work cooperatively so that deaths in drug violence would be better detailed and official crime statistics be more reliable.