The mayor of a violent Mexican border city said Monday he fears a shooting that killed 16 people in a working class neighborhood may have been random because many of the victims were "good kids" with no apparent ties to drug gangs.

The dead included at least eight teenagers, the youngest a 13-year-old girl.

Mayor Jose Reyes Ferriz said police were pursuing all lines of investigation. But he said none of the victims of the attack Saturday night had criminal records, and the teenagers were "good kids, students, athletes."

He said he feared violence was reaching levels of brutality shocking even for Ciudad Juarez, which faces El Paso, Texas, and has become one of the world's deadliest cities amid rampant battles between drug gangs fighting for turf and smuggling routes north.

"There is no logical explanation, a concrete reason for this event. This is something that worries us, gratuitous or random criminal acts," Reyes told MVS Radio. "It goes way beyond what had been happening and puts Ciudad Juarez in even greater danger."

Witnesses and relatives said armed men in two trucks blocked off a dead end street in Villas de Salvarcar, a neighborhood of modest cinderblock homes partly surrounded by a fence topped by barbed wire. The gunmen opened fire at three houses, ending their rampage at one home where young people had been gathered for a party.

Ten people were found dead at the scene and six died at hospitals.

One father rushed into the third home after seeing the gunmen and warned the teenagers to flee, according to Mari Cruz, who lost a son and nephew in the attack, and who heard the details from a girl who survived by hiding in a closet. The father was shot at the entrance and the gunmen forced the young people into a corner of the house before shooting them.

She said her son, Jose Luis Aguilar Camargo, and his cousin, Alberto Soto Camargo, both 19, were students at the Autonomous University of Ciudad Juarez.

"Who did it? Why such hate?" Cruz wailed as tearful neighbors tried to comfort her outside her house. "They were just boys who were not in any gangs."

Next door, friends had made a makeshift altar for Jose Adrian Encina, a 17-year-old high school student. It included a collage of photos of the teenager, including one where he held up a sign reading, "Do you love me?"

Friends outside the home worked on a poster reading, "We will always remember you. You will always be in our hearts. You'll be an angel for all of us."

A girl who gave only her first name, Linda, out of fear for her safety, said Encina was her cousin. She described him as a good student who aspired to be a doctor and had received an academic recognition award from Chihuahua Gov. Jose Reyes Baez.

Three bloody shoes still lay outside the home where the party was held.

Authorities have offered a reward of $76,200 for information leading to the capture of the gunmen. Reyes said police have received five calls with tips that could be useful, but he did not elaborate.

"The people of Juarez must demand that this is investigated thoroughly and we must demand justice for such deplorable crimes," he said at a news conference later Monday.

In another attack in Ciudad Juarez on Monday, armed men burst into a bar around dawn and killed four men and a woman, said Arturo Sandoval, a spokesman for the regional prosecutors' office.

More than 2,600 people were killed last year alone in Ciudad Juarez, a city of 1.3 million people. Authorities say most of the dead have ties to drug gangs but civilians have been caught in the cross fire in increasing numbers. Among the dead last year were university professors and an honor student.

Elsewhere, gunmen killed 10 people and wounded 15 in a bar in Torreon, a city in the northern state of Coahuila.

Drug violence has surged in many parts of Mexico since President Felipe Calderon deployed thousands of troops in 2006 to crush powerful cartels. More than 15,000 people have been killed in gang violence since.