Mexican authorities dug up a muddy mass grave near Mexico City and were investigating Thursday if the remains belong to 12 young people whose kidnapping in May shocked the capital.
Mexico City's top prosecutor, Rodolfo Rios, said the remains of seven people have been recovered since the search began in a park on Wednesday and that workers are still digging for more bodies.
Federal authorities have detained two people who were near the mass grave that was discovered at the park in the municipality of Tlalmanalco, some 30 kilometers (19 miles) southeast of the capital, Rios said.
The victims were kidnapped from a downtown bar in broad daylight on a Sunday morning three months ago in a case that raised concerns about security in Mexico City, which has been relatively immune from the country's drug cartel violence.
Rios did not indicate how the mass grave was discovered, only saying that it was found thanks to collaboration with federal prosecutors. Police put up a checkpoint on a dirt road surrounded by corn fields more than one kilometer from the site to block access.
"For the moment seven bodies have been found in a pit," Rios told a news conference, stressing that it would take at least two days to get results from DNA tests to identify the victims.
An official from the federal attorney general's office told AFP that the remains were mere bones, making it difficult for now to determine if they are male or female or the cause of death.
A lawyer representing the kidnap victims' families, Ricardo Martinez, said a police officer who was at the site told him that 13 bodies were found after the two detainees took authorities to the grave.
"According to the people who spoke with me and others I spoke with, I wouldn't doubt that it is them (the kidnap victims)," Martinez told Milenio television.
Rios has linked the mass kidnapping to a dispute between two gangs known as La Union and Tepis, which sell drugs in the city's rough Tepito neighborhood. But Mexico City authorities insist that the bigger cartels do not operate in the capital.
Most of those abducted hail from Tepito and two of them, including 16-year-old Jerzy Ortiz, are sons of jailed criminals. But their families insist that the youngsters are not involved in criminal activities.
The group was whisked away by 17 men who walked into the Heaven bar on May 26 and took them away in several cars, just blocks away from the federal police headquarters and the US embassy, according to footage from security cameras.
Two bar owners have been arrested in connection with the case. The charred remains of a third associate was found in the central state of Morelos last month.
Rios met with relatives of victims before his news conference. Earlier Jerzy's aunt, Eugenia Ponce Ramos, told AFP that Rios had telephoned the families and told them that authorities have yet to identify the remains.
"We have to stay calm," said Ponce, who is among scores of family members who have held protests in the capital to demand answers about the fate of their loved ones.
Mexico City authorities initially classified the disappearances as a missing persons case before determining it was a mass kidnapping.
Officials have since offered a reward of more than $750,000 for information that could help the investigation.
Heaven is an after-hours bar that was briefly closed in 2011 after a man vanished.
But Mexico City Mayor Miguel Angel Mancera insists that the mass kidnapping is an "isolated" case linked to local gangs.
The former Mexico City police chief, Manuel Mondragon y Kalb, who now heads the federal police, told Mexican television last month that the country's main gangs have "crystalized" in some areas of the capital.