| The interior secretary has promised to step up troop and police presence in the area where the latest killings occurred
The toll of murder victims buried in a series of mass graves in northern Mexico has risen to 116, according to Mexico's attorney general who blames the atrocity on the Zetas drug cartel.
Soldiers found the corpses last week in San Fernando in Tamaulipas state near Texas and initially unearthed 59 bodies, but the toll has since risen steadily in one of the most gruesome finds so far in Mexico's escalating drug war.
"Today we can confirm the discovery of a total of 116 people killed in this criminal act ... by the Zetas," Marisela Morales, the attorney general, announced on Tuesday in Mexico City.
The body count could still rise and Mexican media said 128 corpses had now been recovered in San Fernando.
Authorities in Tamaulipas declined to comment on the figure.
San Fernando is a town about 145km south of Brownsville, Texas, on a well-travelled stretch of highway that runs near the Gulf Coast. It is an area regularly patrolled by the Mexican military.
Francisco Blake Mora, the Mexican interior secretary, pledged to step up the presence of troops and federal police in the area where the killings occurred and not leave the area until the killers and drug gang members there have been caught.
"Organised crime, in its desperation, resorts to committing atrocities that we can't and shouldn't tolerate as a government and as a society," Blake said.
More than 37,000 people have been killed since Felipe Calderon, the president, sent in the army to fight the drug gangs in 2006, worrying the US and some investors and tarnishing Mexico's international image as a favoured tourist destination.
The victims in Tamaulipas, one of the drug war's worst flash-points, may have been killed after refusing to work for the Zetas, according to media reports.
The gang is increasingly making a name for itself as the most violent of Mexico's powerful cartels.
Morales said 17 suspects had been arrested in the government's investigation, but she declined to give more details about any possible motives for the massacre or the identities of the victims.
The graves were near a ranch where 72 Central and South American migrants were killed last year by the Zetas preying on undocumented migrants heading north in search of work in the US.
Guatemala's foreign ministry said this week one of its citizens was among the dead in Tamaulipas. It is unclear how many were illegal immigrants, who are being targeted for kidnap by drug gangs seeking to hold them to ransom.
The Zetas and rival Gulf Cartel are fighting in Tamaulipas over lucrative drug transit routes to the US.
Authorities are working to identify the bodies, one of which may belong to a US citizen, through DNA samples and other techniques.
Mexico and the US have accused each other of hindering progress, straining diplomatic relations to the point where the US ambassador to Mexico resigned last month.