Gunmen stormed a party packed with teenage revelers in Ciudad Juarez early Sunday, killing at least 13 people in the latest spasm of violence to slam the border city, authorities said.

Officials in the northern state of Chihuahua said high school students and others were at a private home celebrating a school soccer victory when armed men rolled up in seven vehicles and opened fire.

Eleven of the dead were under 20, officials said. At least 10 others were reported wounded.

The motive was not immediately clear. But gatherings in Ciudad Juarez and other Mexican cities have been attacked before as warring gangs pursue targets amid a nationwide drug war.

El Diario, a daily newspaper in Ciudad Juarez, reported on its website that one of the slain teens was a witness in a multiple homicide.

Ciudad Juarez has been the most violent corner in Mexico during the last two years, with more than 3,700 people slain as two drug gangs have waged a ferocious battle for control of the important cross-border smuggling passage into nearby El Paso.

Hit men in Ciudad Juarez have even hunted down their victims in fly-by-night drug-rehabilitation centers. In one attack last year, gunmen killed 18 men in a treatment center.

The killings have shown no signs of letting up in the new year. More than 175 people have been slain in the city already in 2010, according to unofficial tallies by the Mexico media outlets.

The stubbornness and severity of the violence in Ciudad Juarez have flummoxed the government of Mexican President Felipe Calderon, which declared a war on drug cartels three years ago.

Early last year, the government created a force of nearly 10,000 military troops and federal police to patrol the city’s streets in an attempt to bring the killing under control while a new local police force was being built. But after a brief dip in slayings, the murder rate soared during the second half of 2009, and the death toll of more than 2,000 topped that of a year earlier.

Last month, the Calderon administration tried a new tack. Amid widespread complaints that soldiers were trampling people’s rights, the government decided to reduce the army’s profile by pulling troops off the streets and sent in 3,000 more federal police officers to carry out patrolling and investigative duties.

Elsewhere in Mexico on Sunday, gunmen in a convoy attacked a police station with assault rifles and fragmentation grenades in the port city of Lazaro Cardenas, killing a police officer and two civilians, Mexican media reported. The Pacific Coast city is in Michoacan, Calderon’s home state and a violent front in the drug war.

ken.ellingwood@latimes.com

Cecilia Sanchez in The Times’ Mexico City Bureau contributed to this report.