Mexico City: Investigators have found 31 bodies in a clandestine grave in the southern part of the Mexican Gulf state of Veracruz, military spokesmen said.
The grave was found Tuesday at the El Diamante ranch in the Tres Valles region, which is on the border with Oaxaca state.
Officials initially said "many bodies" had been found at the ranch and later put the number of bodies at 28.
Marines are "guarding the area", while investigators are gathering evidence, deputy regional prosecutor Arturo Herrera Cantillo said.
An anonymous telephone tip led police to the mass grave, Cantillo told Mexican media.
Anyone with relatives or friends who went missing in the past month to six weeks should contact the prosecutor`s office, Herrera Cantillo said.
Thousands of migrants headed for the US pass through Veracruz each year, and drug traffickers use smuggling routes in the state to move narcotics into Mexico`s northern neighbour.
The federal government expanded its presence in neighbouring Tamaulipas state in May to fight the Los Zetas and Gulf drug cartels, which have unleashed a wave of violence in the region.
Veracruz`s government has stepped up patrols along the border to prevent the cartels from moving into its territory.
The state government has been working with the army and marines to hunt down the members of criminal organisations, especially those involved in kidnappings, this year.
Veracruz, Mexico`s third most populous state, has been plagued by a turf war between rival drug cartels that has sent the murder rate skyrocketing in the past few years.
The Gulf, Los Zetas and Jalisco Nueva Generacion cartels, as well as breakaway members of the once powerful Familia Michoacana organisation, are fuelling the violence in the state.
The port city of Veracruz will be the site of the 24th Ibero-American Summit of heads of state and government and will host the 22nd Central American and Caribbean Games later this year.