CIUDAD JUAREZ, Mexico – Gunmen stormed two neighboring homes and massacred 13 young people at a birthday party in the latest large-scale attack in this violent border city, even as a new government strategy seeks to restore order with social programs and massive police deployments.

Attackers in two vehicles pulled up to the houses in a lower-middle-class Ciudad Juarez neighborhood late Friday and opened fire on about four dozen partygoers gathered for a 15-year-old boy’s birthday party.

The dead identified so far were 13 to 32 years old, including six women and girls, Chihuahua state Attorney General Carlos Salas said. He said 20 people were wounded, including a 9-year-old boy. Most of the victims were high school students, a survivor said.

Relatives gathered outside the prosecutor’s office, some weeping laments, some shouting demands for justice. All asked not to be identified for fear of reprisals.

“Why, my God, why,” shouted the mother of Daniel Figueroa, 16, after she identified her son’s body.

“I want to be dead, with my daughter,” said the mother of a 19-year-old woman killed in the attack. “This cannot go on. We want justice, even though nothing can bring her back.”

Residents of Ciudad Juarez, one of the world’s deadliest cities, no longer go out much to celebrate because of a violent turf war between the Sinaloa and Juarez cartels, who frequently attack their rivals in bars, restaurants, drug rehab centers and other public places.

A survivor said an attacker entered one of the homes and asked partygoers about a car parked out front, suggesting the killers may have been following the vehicle. The 16-year-old survived the attack by throwing himself to the floor and other partygoers fell on top of him, shielding him from the bullets.

The teenager said the gunman he saw appeared to be about 20, wearing a baseball cap and carrying a pistol, and simply opened fire after no one answered his questions.