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Vans belonging to authorities arrive at a ranch where a mass grave was found in Tlalmanalco, Mexico on Thursday. It's believed it holds at least some of the 12 people who were abducted from a bar in an upscale area of the capital nearly three months ago. (Ivan Pierre Aguirre/AP)

A mass grave discovered east of Mexico City may contain some of the 12 people who vanished from a bar in an upscale area of the capital nearly three months ago, Mexican authorities said Thursday.

At least seven corpses had been recovered from the grave on private property in Tlalmanalco, Mexico City prosecutor Rodolfo Rios told reporters at a news conference. He said the victims could not be identified from clothing, and the cause of death had not been determined.

"We will look at DNA tests that have been taken … to confirm or discard scientifically if the bodies found are the people who disappeared from the bar," Rios said.

The federal Attorney General's Office said agents had received information about possible illegal weapons on the property known locally as Rancho La Negra, and obtained a search warrant. When they started looking around, they discovered the grave, Renato Sales Heredia, an assistant attorney general, told reporters.

"They found a home that looked like a safe house," Attorney General Jesus Murillo Karam told reporters. "We were operating under the belief it was a weapons case."

'We are dying every day'

The young bar-goers vanished from the after-hours Heaven club at midday May 26, just a block from Mexico City's leafy Paseo de Reforma, the capital's equivalent of Paris's Champs-Élysées. Some of their relatives showed up on the property being excavated, crying and covering their faces from the media.

"We have had three months with this anxiety," Maria Teresa Ramos, grandmother of Jerzy Ortiz, one of the missing, told Milenio television. "We are dying every day, little by little."

One federal investigator at the scene said searchers were "90 per cent sure" that the bodies belonged to the victims in the Heaven case.

Prosecutors have said the abductions from the bar were linked to a dispute between two rival drug gangs, one in Mexico City's dangerous Tepito neighbourhood, home to most of the abducted. The families of the disappeared say the missing young people were not involved in drug trafficking.

Surveillance cameras showed several cars pulling up to the bar and taking the victims away. The 12 have not been heard from since.

So far, five people have been detained in the Heaven case, including club owner Ernesto Espinosa Lobo, known as "The Wolf," who has been charged with kidnapping. Among the arrested are another bar owner, a driver and security guard.

The mass abduction mirrored crimes in drug-trafficking hot spots such as the western state of Michoacan, where 21 tourists disappeared, only to be found in a mass grave, or in Monterrey, where 17 kidnapped musicians were found dead at the bottom of a well.