Updated

Families of 12 young people who were kidnapped from a Mexico City bar in May waited anxiously Friday to learn if a mass grave near the capital contained their sons and daughters.

Investigators found seven decomposed bodies on a ranch southeast of the city Thursday and dug through the night to look for more, but officials warned it would take at least two days to identify the remains.

"The excavation continues to check if there are more bodies," Mexico City's top prosecutor, Rodolfo Rios, told MVS Radio, adding that the cause of death remains unknown.

The abductees, aged 16 to 34, were taken from a downtown bar in broad daylight three months ago, marring the capital's image as an oasis from the country's raging drug violence.

They were kidnapped at the Heaven after-hours bar by a group of men who escorted them to several cars one Sunday morning. The bar is a short walk from a federal police building and the US embassy near the busy Reforma Boulevard.

Most of the kidnap victims hail from the city's rough Tepito neighborhood, notorious for a busy market packed with contraband goods, pickpockets and small gangs.

Prosecutors have linked the mass abduction to a dispute between two gangs known as La Union and Tepis.

Mass kidnappings and mass graves are more common near the US border, but authorities insist that the country's bigger cartels do not operate in Mexico City.

Two of the kidnap victims are sons of men jailed for being gang members, but their parents insist they never followed their fathers' footsteps.

One of them is 16-year-old Jerzy Ortiz, son of Jorge Ortiz Reyes, alias "The Tank," who was sentenced to 23 years in prison in 2003.

"We are very tense, thinking about all sorts of things," the 16-year-old's aunt, Eugenia Ponce Ramos, told AFP. "It has been an agony 24 hours a day and now it is more intense."

The families have held protests to demand answers about the case and they barged into a press conference by Rios on Thursday when he was about to discuss the mass grave.

Rios said he has told the families that "as long as we are not certain they are dead, there is hope they are alive. So we continue to work to find them alive."

Two bar owners have been arrested, while the charred remains of a third associate were found in the central state of Morelos last month after a gangland-style murder.

Now relatives must wait for news on the discovery made at the Rancho La Mesa ecological park in the municipality of Tlalmanalco, a mountainous area of pine trees, corn fields and humble rural homes 30 kilometers (19 miles) from the capital.

A federal police officer at the scene told AFP that authorities had searched a ranch for weapons on Wednesday, finding firearms in a parked trailer and a stretch of land covered in cement.

"We began to dig and found the bodies," he said.

A lawyer representing some victims' relatives, Ricardo Martinez, said Thursday he "wouldn't doubt" the remains are of the 12 young people after speaking with a police officer who was at the site.